[media] bttv: don't setup the controls if there are no video devices

The no_video flag was checked in all other cases except one. Calling
v4l2_ctrl_handler_setup() if no_video is 1 will crash.
This wasn't noticed before since there are only two card types that
set no_video to 1, so this type of hardware is quite rare.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reported-by: Lorenz Röhrl <sheepshit@gmx.de>
Tested-by: Lorenz Röhrl <sheepshit@gmx.de>
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>