HID: cp2112: fix broken gpio_direction_input callback

When everything goes smoothly, ret is set to 0 which makes the function
to return EIO error.

Fixes: 8e9faa15

 ("HID: cp2112: fix gpio-callback error handling")
Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>