cpu/stm32f1: Reduce scope of ret variable in spi_transfer_bytes.
cpu/stm32f1: Reduce scope of ret variable in spi_transfer_bytes.

Reduced scope to inside the while loop as per comments in RIOT-OS/RIOT#1630

Signed-off-by: Joakim Gebart <f390e101598f080a05d01e0128f32a81cb56bd9b@gebart.se>

smlng/RIOT,beurdouche/RIOT,herrfz/RIOT,robixnai/RIOT,ks156/RIOT,adrianghc/RIOT,jhollister/RIOT,immesys/RiSyn,aeneby/RIOT,kYc0o/RIOT,shady33/RIOT,syin2/RIOT,watr-li/RIOT,ThanhVic/RIOT,biboc/RIOT,daniel-k/RIOT,luciotorre/RIOT,Osblouf/RIOT,kaleb-himes/RIOT,kb2ma/RIOT,lazytech-org/RIOT,immesys/RiSyn,chris-wood/RIOT,rfuentess/RIOT,openkosmosorg/RIOT,asanka-code/RIOT,MonsterCode8000/RIOT,Yonezawa-T2/RIOT,asanka-code/RIOT,toonst/RIOT,hamilton-mote/RIOT-OS,beurdouche/RIOT,rousselk/RIOT,herrfz/RIOT,tfar/RIOT,Hyungsin/RIOT-OS,daniel-k/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,khhhh/RIOT,Josar/RIOT,centurysys/RIOT,jfischer-phytec-iot/RIOT,toonst/RIOT,marcosalm/RIOT,EmuxEvans/RIOT,sgso/RIOT,openkosmosorg/RIOT,1blankz7/RIOT,hamilton-mote/RIOT-OS,alignan/RIOT,kbumsik/RIOT,jfischer-phytec-iot/RIOT,Lotterleben/RIOT,alex1818/RIOT,emmanuelsearch/RIOT,bartfaizoltan/RIOT,bartfaizoltan/RIOT,kushalsingh007/RIOT,x3ro/RIOT,Josar/RIOT,dailab/RIOT,rfuentess/RIOT,benoit-canet/RIOT,watr-li/RIOT,adrianghc/RIOT,cladmi/RIOT,rousselk/RIOT,yogo1212/RIOT,kb2ma/RIOT,jfischer-phytec-iot/RIOT,LudwigOrtmann/RIOT,avmelnikoff/RIOT,alex1818/RIOT,herrfz/RIOT-old,binarylemon/RIOT,FrancescoErmini/RIOT,dhruvvyas90/RIOT,centurysys/RIOT,tdautc19841202/RIOT,abp719/RIOT,ant9000/RIOT,jhollister/RIOT,thiagohd/RIOT,Hyungsin/RIOT-OS,rakendrathapa/RIOT,jremmert-phytec-iot/RIOT,OTAkeys/RIOT,LudwigKnuepfer/RIOT,marcosalm/RIOT,jhollister/RIOT,DipSwitch/RIOT,yogo1212/RIOT,abkam07/RIOT,alex1818/RIOT,nsol-nmsu/RIOT,neumodisch/RIOT,MarkXYang/RIOT,kerneltask/RIOT,rfswarm2/RIOT,biboc/RIOT,changbiao/RIOT,ThanhVic/RIOT,aeneby/RIOT,mtausig/RIOT,tdautc19841202/RIOT,ximus/RIOT,EmuxEvans/RIOT,centurysys/RIOT,ximus/RIOT,sgso/RIOT,luciotorre/RIOT,herrfz/RIOT,shady33/RIOT,zhuoshuguo/RIOT,Osblouf/RIOT,A-Paul/RIOT,LudwigOrtmann/RIOT,ntrtrung/RIOT,adjih/RIOT,phiros/RIOT,toonst/RIOT,dkm/RIOT,nsol-nmsu/RIOT,herrfz/RIOT,plushvoxel/RIOT,smlng/RIOT,lazytech-org/RIOT,brettswann/RIOT,JensErdmann/RIOT,mfrey/RIOT,ntrtrung/RIOT,immesys/RiSyn,avmelnikoff/RIOT,roberthartung/RIOT,1blankz7/RIOT,alex1818/RIOT,asanka-code/RIOT,abkam07/RIOT,Lotterleben/RIOT,phiros/RIOT,sumanpanchal/RIOT,MarkXYang/RIOT,chris-wood/RIOT,rfswarm/RIOT,DipSwitch/RIOT,kaleb-himes/RIOT,neumodisch/RIOT,l3nko/RIOT,mtausig/RIOT,koenning/RIOT,latsku/RIOT,zhuoshuguo/RIOT,basilfx/RIOT,adrianghc/RIOT,smlng/RIOT,Yonezawa-T2/RIOT,jbeyerstedt/RIOT-OTA-update,alex1818/RIOT,dailab/RIOT,kerneltask/RIOT,backenklee/RIOT,l3nko/RIOT,locicontrols/RIOT,nsol-nmsu/RIOT,neumodisch/RIOT,MonsterCode8000/RIOT,kb2ma/RIOT,neiljay/RIOT,miri64/RIOT,miri64/RIOT,kerneltask/RIOT,msolters/RIOT,basilfx/RIOT,herrfz/RIOT-old,kb2ma/RIOT,rajma996/RIOT,hamilton-mote/RIOT-OS,dhruvvyas90/RIOT,kbumsik/RIOT,openkosmosorg/RIOT,miri64/RIOT,mziegert/RIOT,kbumsik/RIOT,ximus/RIOT,jhollister/RIOT,syin2/RIOT,x3ro/RIOT,ximus/RIOT,stevenj/RIOT,basilfx/RIOT,katezilla/RIOT,herrfz/RIOT,rfswarm2/RIOT,mtausig/RIOT,backenklee/RIOT,binarylemon/RIOT,benoit-canet/RIOT,rfuentess/RIOT,lebrush/RIOT,RubikonAlpha/RIOT,rajma996/RIOT,kbumsik/RIOT,watr-li/RIOT,daniel-k/RIOT,RIOT-OS/RIOT,herrfz/RIOT-old,avmelnikoff/RIOT,rakendrathapa/RIOT,d00616/RIOT,rakendrathapa/RIOT,OlegHahm/RIOT,patkan/RIOT,OlegHahm/RIOT,luciotorre/RIOT,tfar/RIOT,locicontrols/RIOT,EmuxEvans/RIOT,A-Paul/RIOT,arvindpdmn/RIOT,dkm/RIOT,roberthartung/RIOT,jasonatran/RIOT,OTAkeys/RIOT,immesys/RiSyn,kushalsingh007/RIOT,phiros/RIOT,changbiao/RIOT,rajma996/RIOT,jferreir/RIOT,shady33/RIOT,jasonatran/RIOT,stevenj/RIOT,gebart/RIOT,emmanuelsearch/RIOT,thiagohd/RIOT,gautric/RIOT,centurysys/RIOT,bartfaizoltan/RIOT,attdona/RIOT,Yonezawa-T2/RIOT,roberthartung/RIOT,toonst/RIOT,rakendrathapa/RIOT,alignan/RIOT,RBartz/RIOT,daniel-k/RIOT,d00616/RIOT,jferreir/RIOT,rfswarm2/RIOT,patkan/RIOT,bartfaizoltan/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,latsku/RIOT,brettswann/RIOT,alignan/RIOT,dkm/RIOT,EmuxEvans/RIOT,mziegert/RIOT,katezilla/RIOT,RBartz/RIOT,abp719/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,asanka-code/RIOT,JensErdmann/RIOT,lebrush/RIOT,attdona/RIOT,kbumsik/RIOT,AnonMall/RIOT,altairpearl/RIOT,Darredevil/RIOT,TobiasFredersdorf/RIOT,wentaoshang/RIOT,dhruvvyas90/RIOT,altairpearl/RIOT,authmillenon/RIOT,Yonezawa-T2/RIOT,LudwigKnuepfer/RIOT,luciotorre/RIOT,rfuentess/RIOT,AnonMall/RIOT,Osblouf/RIOT,yogo1212/RIOT,authmillenon/RIOT,kerneltask/RIOT,emmanuelsearch/RIOT,benoit-canet/RIOT,l3nko/RIOT,automote/RIOT,jremmert-phytec-iot/RIOT,OlegHahm/RIOT,thiagohd/RIOT,gautric/RIOT,khhhh/RIOT,rousselk/RIOT,abkam07/RIOT,Lotterleben/RIOT,backenklee/RIOT,rfswarm2/RIOT,koenning/RIOT,altairpearl/RIOT,mziegert/RIOT,thiagohd/RIOT,fnack/RIOT,FrancescoErmini/RIOT,emmanuelsearch/RIOT,Lotterleben/RIOT,latsku/RIOT,rfswarm2/RIOT,phiros/RIOT,fnack/RIOT,arvindpdmn/RIOT,RBartz/RIOT,biboc/RIOT,kaspar030/RIOT,lazytech-org/RIOT,sgso/RIOT,kaleb-himes/RIOT,jferreir/RIOT,Lexandro92/RIOT-CoAP,jbeyerstedt/RIOT-OTA-update,RubikonAlpha/RIOT,jhollister/RIOT,watr-li/RIOT,l3nko/RIOT,phiros/RIOT,Josar/RIOT,lebrush/RIOT,abp719/RIOT,haoyangyu/RIOT,ntrtrung/RIOT,kaleb-himes/RIOT,Lotterleben/RIOT,latsku/RIOT,syin2/RIOT,TobiasFredersdorf/RIOT,attdona/RIOT,neumodisch/RIOT,dhruvvyas90/RIOT,thomaseichinger/RIOT,PSHIVANI/Riot-Code,DipSwitch/RIOT,abkam07/RIOT,jferreir/RIOT,beurdouche/RIOT,PSHIVANI/Riot-Code,FrancescoErmini/RIOT,dkm/RIOT,beurdouche/RIOT,AnonMall/RIOT,koenning/RIOT,kaleb-himes/RIOT,sumanpanchal/RIOT,authmillenon/RIOT,aeneby/RIOT,Hyungsin/RIOT-OS,authmillenon/RIOT,gautric/RIOT,changbiao/RIOT,alignan/RIOT,MarkXYang/RIOT,immesys/RiSyn,khhhh/RIOT,adjih/RIOT,haoyangyu/RIOT,stevenj/RIOT,FrancescoErmini/RIOT,Darredevil/RIOT,1blankz7/RIOT,LudwigKnuepfer/RIOT,rajma996/RIOT,backenklee/RIOT,rousselk/RIOT,abp719/RIOT,lebrush/RIOT,Darredevil/RIOT,centurysys/RIOT,l3nko/RIOT,RIOT-OS/RIOT,automote/RIOT,ant9000/RIOT,abp719/RIOT,Lexandro92/RIOT-CoAP,kb2ma/RIOT,plushvoxel/RIOT,Yonezawa-T2/RIOT,lebrush/RIOT,zhuoshuguo/RIOT,benoit-canet/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,gebart/RIOT,neumodisch/RIOT,katezilla/RIOT,sgso/RIOT,beurdouche/RIOT,attdona/RIOT,locicontrols/RIOT,LudwigOrtmann/RIOT,openkosmosorg/RIOT,koenning/RIOT,malosek/RIOT,immesys/RiSyn,MarkXYang/RIOT,dkm/RIOT,chris-wood/RIOT,latsku/RIOT,neiljay/RIOT,Josar/RIOT,zhuoshuguo/RIOT,gebart/RIOT,miri64/RIOT,luciotorre/RIOT,RubikonAlpha/RIOT,zhuoshuguo/RIOT,khhhh/RIOT,josephnoir/RIOT,basilfx/RIOT,Osblouf/RIOT,miri64/RIOT,changbiao/RIOT,TobiasFredersdorf/RIOT,herrfz/RIOT-old,thomaseichinger/RIOT,ntrtrung/RIOT,RBartz/RIOT,MonsterCode8000/RIOT,Lexandro92/RIOT-CoAP,d00616/RIOT,thomaseichinger/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,haoyangyu/RIOT,sumanpanchal/RIOT,Osblouf/RIOT,abkam07/RIOT,TobiasFredersdorf/RIOT,yogo1212/RIOT,shady33/RIOT,tdautc19841202/RIOT,sgso/RIOT,josephnoir/RIOT,MarkXYang/RIOT,wentaoshang/RIOT,bartfaizoltan/RIOT,phiros/RIOT,plushvoxel/RIOT,mfrey/RIOT,luciotorre/RIOT,jfischer-phytec-iot/RIOT,chris-wood/RIOT,ks156/RIOT,plushvoxel/RIOT,patkan/RIOT,1blankz7/RIOT,aeneby/RIOT,marcosalm/RIOT,neiljay/RIOT,cladmi/RIOT,kYc0o/RIOT,jremmert-phytec-iot/RIOT,robixnai/RIOT,wentaoshang/RIOT,mtausig/RIOT,fnack/RIOT,sumanpanchal/RIOT,d00616/RIOT,jremmert-phytec-iot/RIOT,thiagohd/RIOT,Hyungsin/RIOT-OS,RubikonAlpha/RIOT,nsol-nmsu/RIOT,locicontrols/RIOT,d00616/RIOT,RBartz/RIOT,robixnai/RIOT,Lotterleben/RIOT,jferreir/RIOT,adjih/RIOT,openkosmosorg/RIOT,ntrtrung/RIOT,dailab/RIOT,wentaoshang/RIOT,Ell-i/RIOT,josephnoir/RIOT,PSHIVANI/Riot-Code,wentaoshang/RIOT,RBartz/RIOT,herrfz/RIOT,AnonMall/RIOT,roberthartung/RIOT,altairpearl/RIOT,ThanhVic/RIOT,benoit-canet/RIOT,marcosalm/RIOT,yogo1212/RIOT,EmuxEvans/RIOT,watr-li/RIOT,Yonezawa-T2/RIOT,msolters/RIOT,arvindpdmn/RIOT,syin2/RIOT,ximus/RIOT,ThanhVic/RIOT,ks156/RIOT,kushalsingh007/RIOT,alex1818/RIOT,patkan/RIOT,Lexandro92/RIOT-CoAP,bartfaizoltan/RIOT,x3ro/RIOT,ntrtrung/RIOT,MohmadAyman/RIOT,kerneltask/RIOT,alignan/RIOT,chris-wood/RIOT,nsol-nmsu/RIOT,gbarnett/RIOT,kaspar030/RIOT,hamilton-mote/RIOT-OS,BytesGalore/RIOT,MohmadAyman/RIOT,asanka-code/RIOT,mziegert/RIOT,malosek/RIOT,jasonatran/RIOT,rousselk/RIOT,brettswann/RIOT,binarylemon/RIOT,Darredevil/RIOT,malosek/RIOT,JensErdmann/RIOT,A-Paul/RIOT,stevenj/RIOT,zhuoshuguo/RIOT,fnack/RIOT,rousselk/RIOT,RubikonAlpha/RIOT,ant9000/RIOT,marcosalm/RIOT,avmelnikoff/RIOT,msolters/RIOT,mfrey/RIOT,adjih/RIOT,EmuxEvans/RIOT,automote/RIOT,biboc/RIOT,fnack/RIOT,gebart/RIOT,Ell-i/RIOT,BytesGalore/RIOT,TobiasFredersdorf/RIOT,thiagohd/RIOT,LudwigKnuepfer/RIOT,rakendrathapa/RIOT,BytesGalore/RIOT,authmillenon/RIOT,khhhh/RIOT,tfar/RIOT,d00616/RIOT,binarylemon/RIOT,daniel-k/RIOT,cladmi/RIOT,rakendrathapa/RIOT,backenklee/RIOT,benoit-canet/RIOT,ant9000/RIOT,jbeyerstedt/RIOT-OTA-update,biboc/RIOT,cladmi/RIOT,x3ro/RIOT,smlng/RIOT,MohmadAyman/RIOT,OlegHahm/RIOT,gbarnett/RIOT,Lexandro92/RIOT-CoAP,AnonMall/RIOT,PSHIVANI/Riot-Code,DipSwitch/RIOT,jremmert-phytec-iot/RIOT,brettswann/RIOT,gautric/RIOT,MonsterCode8000/RIOT,lazytech-org/RIOT,changbiao/RIOT,brettswann/RIOT,attdona/RIOT,tdautc19841202/RIOT,rfswarm/RIOT,Ell-i/RIOT,haoyangyu/RIOT,ks156/RIOT,MohmadAyman/RIOT,latsku/RIOT,MonsterCode8000/RIOT,msolters/RIOT,gbarnett/RIOT,1blankz7/RIOT,yogo1212/RIOT,Josar/RIOT,jfischer-phytec-iot/RIOT,aeneby/RIOT,ThanhVic/RIOT,Darredevil/RIOT,robixnai/RIOT,rajma996/RIOT,cladmi/RIOT,gbarnett/RIOT,arvindpdmn/RIOT,stevenj/RIOT,thomaseichinger/RIOT,RubikonAlpha/RIOT,MohmadAyman/RIOT,authmillenon/RIOT,mtausig/RIOT,rajma996/RIOT,automote/RIOT,rfswarm/RIOT,LudwigKnuepfer/RIOT,gbarnett/RIOT,abp719/RIOT,jbeyerstedt/RIOT-OTA-update,khhhh/RIOT,RIOT-OS/RIOT,jbeyerstedt/RIOT-OTA-update,LudwigOrtmann/RIOT,PSHIVANI/Riot-Code,arvindpdmn/RIOT,Ell-i/RIOT,josephnoir/RIOT,katezilla/RIOT,JensErdmann/RIOT,shady33/RIOT,FrancescoErmini/RIOT,kaspar030/RIOT,fnack/RIOT,LudwigOrtmann/RIOT,malosek/RIOT,tfar/RIOT,sgso/RIOT,centurysys/RIOT,brettswann/RIOT,jferreir/RIOT,kYc0o/RIOT,wentaoshang/RIOT,openkosmosorg/RIOT,dhruvvyas90/RIOT,locicontrols/RIOT,MohmadAyman/RIOT,toonst/RIOT,1blankz7/RIOT,kaspar030/RIOT,kYc0o/RIOT,ThanhVic/RIOT,binarylemon/RIOT,adjih/RIOT,smlng/RIOT,binarylemon/RIOT,attdona/RIOT,dhruvvyas90/RIOT,shady33/RIOT,changbiao/RIOT,Ell-i/RIOT,lazytech-org/RIOT,gautric/RIOT,DipSwitch/RIOT,plushvoxel/RIOT,locicontrols/RIOT,neiljay/RIOT,JensErdmann/RIOT,gbarnett/RIOT,koenning/RIOT,haoyangyu/RIOT,x3ro/RIOT,ant9000/RIOT,mziegert/RIOT,automote/RIOT,BytesGalore/RIOT,katezilla/RIOT,kYc0o/RIOT,syin2/RIOT,sumanpanchal/RIOT,asanka-code/RIOT,kushalsingh007/RIOT,MonsterCode8000/RIOT,hamilton-mote/RIOT-OS,stevenj/RIOT,PSHIVANI/Riot-Code,altairpearl/RIOT,Hyungsin/RIOT-OS,emmanuelsearch/RIOT,malosek/RIOT,A-Paul/RIOT,rfuentess/RIOT,mziegert/RIOT,kushalsingh007/RIOT,OTAkeys/RIOT,arvindpdmn/RIOT,herrfz/RIOT-old,watr-li/RIOT,mfrey/RIOT,mfrey/RIOT,Darredevil/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,altairpearl/RIOT,gebart/RIOT,OTAkeys/RIOT,emmanuelsearch/RIOT,rfswarm/RIOT,neiljay/RIOT,chris-wood/RIOT,DipSwitch/RIOT,marcosalm/RIOT,RIOT-OS/RIOT,malosek/RIOT,rfswarm2/RIOT,ximus/RIOT,OTAkeys/RIOT,A-Paul/RIOT,tdautc19841202/RIOT,lebrush/RIOT,haoyangyu/RIOT,kaspar030/RIOT,kushalsingh007/RIOT,koenning/RIOT,Lexandro92/RIOT-CoAP,dailab/RIOT,JensErdmann/RIOT,roberthartung/RIOT,ks156/RIOT,daniel-k/RIOT,jasonatran/RIOT,jremmert-phytec-iot/RIOT,msolters/RIOT,LudwigOrtmann/RIOT,josephnoir/RIOT,FrancescoErmini/RIOT,MarkXYang/RIOT,adrianghc/RIOT,sumanpanchal/RIOT,tdautc19841202/RIOT,automote/RIOT,avmelnikoff/RIOT,rfswarm/RIOT,locicontrols/RIOT,robixnai/RIOT,thomaseichinger/RIOT,jhollister/RIOT,msolters/RIOT,OlegHahm/RIOT,rfswarm/RIOT,dailab/RIOT,BytesGalore/RIOT,AnonMall/RIOT,basilfx/RIOT,patkan/RIOT,neumodisch/RIOT,patkan/RIOT,Osblouf/RIOT,Lotterleben/RIOT,tfar/RIOT,adrianghc/RIOT,abkam07/RIOT,robixnai/RIOT,l3nko/RIOT