cpu, atmega_common: fix returns and error codes in periph/i2c
cpu, atmega_common: fix returns and error codes in periph/i2c

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