greybus: gpio: remove overly defensive argument verification

Remove overly defensive argument verification in gpio-chip callbacks. We
should trust gpiolib to get this right (or we would not even get any
callback) just like the other gpio drivers do.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>