[media] v4l2-ctrls.h: add to device-drivers DocBook

The comments there are using a wrong format. Due to that,
DocBook were unable to parse it.

Fix the tags format, and add it to device-drivers.xml.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>