[media] uvcvideo: GET_RES should only be checked for BITMAP type menu controls

Currently it is also being checked for non BITMAP type menu controls,
breaking the logitech LED control menu added by uvcdynctrl, as well as
potentially breaking the powerline frequency menu.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>