mraa.c: do not check return value of mraa_gpio_dir when used on muxes
mraa.c: do not check return value of mraa_gpio_dir when used on muxes

Doing so breaks galileo gen2 (gpio2) and others. Failing early is rather
pointless in any case so we may as well attempt the write, muxes do not
neccesarily have directions that work

Fixes #68

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

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