[media] Fix DV_TIMINGS_CAP documentation

This patch fixes the DV_TIMINGS_CAP documentation: part of it was copy-and-paste from
the ENUM_DV_TIMINGS documentation.

Regards,

	Hans

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