V4L/DVB: uvcvideo: Blacklist gain control for Asus EeePC T91 integrated webcam

The Asus EeePC T91 integrated webcam exposes a gain control in the
processing unit but stalls when the control is queried. Blacklist the
gain control for that camera.

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