Revert back to stianeikeland/go-rpio from youngkin/go-rpio fork

The stianeikeland/go-rpio repo was missing support for balanced mode PWM. It was added to the youngkin/go-rpio fork. Once the youngkin/go-rpio changes were merged into stianeikeland/go-rpio this project was modified to revert back to the stianeikeland/go-rpio repo.