Input: gameport - make gameport_register_driver() return errors

Perform actual driver registration right in gameport_register_driver()
instead of offloading it to kgameportd and return proper error code to
callers if driver registration fails.

Note that driver <-> port matching is still done by kgameportd.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>