[media] v4l2-dev: forgot to add VIDIOC_DV_TIMINGS_CAP

The VIDIOC_DV_TIMINGS_CAP ioctl check wasn't added to determine_valid_ioctls().
This caused this ioctl to always return -ENOTTY.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>