Make error check code simpler for libusb1 backend.
Make error check code simpler for libusb1 backend.

And return the python integer instead of a c_int instance.

karlp/pyusb,AlanJAS/pyusb,makerbot/pyusb,kopchik/pyusb,swinman/pyusb,makerbot/pyusb,karlp/pyusb,AlanJAS/pyusb,h3nj3/pyusb,rabryan/pyusb,h3nj3/pyusb,swinman/pyusb,rabryan/pyusb,kopchik/pyusb