i2c.h: Fix docs that incorectly states -1 is failure
i2c.h: Fix docs that incorectly states -1 is failure

Fixes #228

Signed-off-by: Brendan Le Foll <3e0e8c4069934e8b47d99704927a85c66c0ceb33@intel.com>

yoyojacky/mraa,pctj101/mraa,Hbrinj/mraa,Hbrinj/mraa,SyrianSpock/mraa,noahchense/mraa,arunlee77/mraa,KurtE/mraa,jontrulson/mraa,arunlee77/mraa,alex1818/mraa,anonymouse64/mraa,pctj101/mraa,andreivasiliu2211/mraa,sundw2014/mraa,damcclos/mraa,alexandru-elisei/mraa,malikabhi05/mraa,yongli3/mraa,tripzero/mraa,arfoll/mraa,neuroidss/mraa,spitfire88/mraa,mircea/mraa,ProfFan/mraa,alext-mkrs/mraa,sergev/mraa,intel-iot-devkit/mraa,neuberfran/mraa,intel-iot-devkit/mraa,stefan-andritoiu/mraa,pctj101/mraa,arunlee77/mraa,alext-mkrs/mraa,Jon-ICS/mraa,malikabhi05/mraa,arfoll/mraa,neuroidss/mraa,alext-mkrs/mraa,yoyojacky/mraa,matt-auld/mraa,SyrianSpock/mraa,jontrulson/mraa,damcclos/mraa,intel-iot-devkit/mraa,ncrastanaren/mraa,neuberfran/mraa,ncrastanaren/mraa,malikabhi05/mraa,allela-roy/mraa,allela-roy/mraa,sergev/mraa,allela-roy/mraa,stefan-andritoiu/mraa-gpio-chardev,KurtE/mraa,alex1818/mraa,SyrianSpock/mraa,nioinnovation/mraa,andreivasiliu2211/mraa,Pillar1989/mraa,anonymouse64/mraa,Kiritoalex/mraa,STANAPO/mraa,malikabhi05/mraa,g-vidal/mraa,Propanu/mraa,KurtE/mraa,alext-mkrs/mraa,stefan-andritoiu/mraa-gpio-chardev,neuroidss/mraa,sundw2014/mraa,noahchense/mraa,alexandru-elisei/mraa,tripzero/mraa,whbruce/mraa,stefan-andritoiu/mraa-gpio-chardev,intel-iot-devkit/mraa,sundw2014/mraa,Meirtz/mraa,alexandru-elisei/mraa,ncrastanaren/mraa,petreeftime/mraa,stefan-andritoiu/mraa,pctj101/mraa,Jon-ICS/mraa,arfoll/mraa,g-vidal/mraa,ProfFan/mraa,petreeftime/mraa,w4ilun/mraa,matt-auld/mraa,sergev/mraa,petreeftime/mraa,ProfFan/mraa,andreivasiliu2211/mraa,STANAPO/mraa,KurtE/mraa,Kiritoalex/mraa,Kiritoalex/mraa,zBMNForks/mraa,w4ilun/mraa,Hbrinj/mraa,sundw2014/mraa,spitfire88/mraa,whbruce/mraa,noahchense/mraa,intel-iot-devkit/mraa,arfoll/mraa,Pillar1989/mraa,ProfFan/mraa,petreeftime/mraa,Hbrinj/mraa,neuberfran/mraa,zBMNForks/mraa,spitfire88/mraa,yongli3/mraa,smileboywtu/mraa,zBMNForks/mraa,matt-auld/mraa,nioinnovation/mraa,neuberfran/mraa,arfoll/mraa,alexandru-elisei/mraa,damcclos/mraa,smileboywtu/mraa,nioinnovation/mraa,jontrulson/mraa,noahchense/mraa,stefan-andritoiu/mraa,sergev/mraa,stefan-andritoiu/mraa,alext-mkrs/mraa,whbruce/mraa,malikabhi05/mraa,tripzero/mraa,jontrulson/mraa,g-vidal/mraa,mircea/mraa,sergev/mraa,yongli3/mraa,yoyojacky/mraa,anonymouse64/mraa,stefan-andritoiu/mraa,stefan-andritoiu/mraa-gpio-chardev,ncrastanaren/mraa,Propanu/mraa,g-vidal/mraa,sundw2014/mraa,stefan-andritoiu/mraa-gpio-chardev,jontrulson/mraa,andreivasiliu2211/mraa,yongli3/mraa,pctj101/mraa,smileboywtu/mraa,g-vidal/mraa,neuberfran/mraa,ncrastanaren/mraa,Propanu/mraa,Pillar1989/mraa,arunlee77/mraa,spitfire88/mraa,Meirtz/mraa,alex1818/mraa,mircea/mraa,Meirtz/mraa,w4ilun/mraa,KurtE/mraa,STANAPO/mraa,w4ilun/mraa,noahchense/mraa,yongli3/mraa,alexandru-elisei/mraa,Propanu/mraa,Propanu/mraa,Jon-ICS/mraa,whbruce/mraa