cpu: stm32f4: i2c: fix some problems
cpu: stm32f4: i2c: fix some problems

yogo1212/RIOT,A-Paul/RIOT,jasonatran/RIOT,miri64/RIOT,immesys/RiSyn,OlegHahm/RIOT,kaspar030/RIOT,smlng/RIOT,basilfx/RIOT,OTAkeys/RIOT,miri64/RIOT,RIOT-OS/RIOT,basilfx/RIOT,kbumsik/RIOT,OlegHahm/RIOT,jasonatran/RIOT,authmillenon/RIOT,Josar/RIOT,biboc/RIOT,kaspar030/RIOT,kaspar030/RIOT,smlng/RIOT,ks156/RIOT,BytesGalore/RIOT,LudwigKnuepfer/RIOT,hamilton-mote/RIOT-OS,neiljay/RIOT,LudwigOrtmann/RIOT,x3ro/RIOT,ant9000/RIOT,jasonatran/RIOT,kbumsik/RIOT,avmelnikoff/RIOT,adrianghc/RIOT,kbumsik/RIOT,immesys/RiSyn,biboc/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,beurdouche/RIOT,LudwigKnuepfer/RIOT,josephnoir/RIOT,yogo1212/RIOT,mfrey/RIOT,miri64/RIOT,beurdouche/RIOT,cladmi/RIOT,RIOT-OS/RIOT,basilfx/RIOT,lazytech-org/RIOT,lazytech-org/RIOT,jasonatran/RIOT,x3ro/RIOT,kbumsik/RIOT,smlng/RIOT,LudwigKnuepfer/RIOT,avmelnikoff/RIOT,aeneby/RIOT,ant9000/RIOT,cladmi/RIOT,adrianghc/RIOT,OTAkeys/RIOT,immesys/RiSyn,adjih/RIOT,josephnoir/RIOT,Josar/RIOT,authmillenon/RIOT,A-Paul/RIOT,jasonatran/RIOT,mfrey/RIOT,avmelnikoff/RIOT,gebart/RIOT,roberthartung/RIOT,kYc0o/RIOT,toonst/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,Josar/RIOT,kYc0o/RIOT,LudwigOrtmann/RIOT,gebart/RIOT,LudwigOrtmann/RIOT,beurdouche/RIOT,basilfx/RIOT,cladmi/RIOT,A-Paul/RIOT,x3ro/RIOT,RIOT-OS/RIOT,mfrey/RIOT,beurdouche/RIOT,toonst/RIOT,kerneltask/RIOT,OTAkeys/RIOT,basilfx/RIOT,OlegHahm/RIOT,LudwigKnuepfer/RIOT,A-Paul/RIOT,adjih/RIOT,BytesGalore/RIOT,yogo1212/RIOT,gebart/RIOT,rfuentess/RIOT,hamilton-mote/RIOT-OS,avmelnikoff/RIOT,OlegHahm/RIOT,BytesGalore/RIOT,gebart/RIOT,rfuentess/RIOT,LudwigKnuepfer/RIOT,yogo1212/RIOT,immesys/RiSyn,gebart/RIOT,rfuentess/RIOT,ks156/RIOT,lazytech-org/RIOT,ks156/RIOT,avmelnikoff/RIOT,josephnoir/RIOT,Josar/RIOT,aeneby/RIOT,kYc0o/RIOT,rfuentess/RIOT,immesys/RiSyn,yogo1212/RIOT,aeneby/RIOT,aeneby/RIOT,kaspar030/RIOT,mtausig/RIOT,authmillenon/RIOT,immesys/RiSyn,mtausig/RIOT,lazytech-org/RIOT,yogo1212/RIOT,miri64/RIOT,neiljay/RIOT,x3ro/RIOT,hamilton-mote/RIOT-OS,neiljay/RIOT,neiljay/RIOT,roberthartung/RIOT,roberthartung/RIOT,authmillenon/RIOT,lazytech-org/RIOT,biboc/RIOT,LudwigOrtmann/RIOT,kYc0o/RIOT,adjih/RIOT,ks156/RIOT,smlng/RIOT,authmillenon/RIOT,ks156/RIOT,ant9000/RIOT,kerneltask/RIOT,adjih/RIOT,roberthartung/RIOT,mfrey/RIOT,kYc0o/RIOT,adrianghc/RIOT,adrianghc/RIOT,cladmi/RIOT,mtausig/RIOT,biboc/RIOT,roberthartung/RIOT,toonst/RIOT,kerneltask/RIOT,LudwigOrtmann/RIOT,mfrey/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kerneltask/RIOT,mtausig/RIOT,BytesGalore/RIOT,toonst/RIOT,adjih/RIOT,LudwigOrtmann/RIOT,neiljay/RIOT,BytesGalore/RIOT,ant9000/RIOT,kerneltask/RIOT,josephnoir/RIOT,smlng/RIOT,toonst/RIOT,mtausig/RIOT,beurdouche/RIOT,aeneby/RIOT,hamilton-mote/RIOT-OS,biboc/RIOT,A-Paul/RIOT,authmillenon/RIOT,adrianghc/RIOT,kaspar030/RIOT,cladmi/RIOT,kbumsik/RIOT,miri64/RIOT,hamilton-mote/RIOT-OS,rfuentess/RIOT,ant9000/RIOT,Josar/RIOT,x3ro/RIOT