[media] v4l2-subdev: reorder the v4l2_subdev_video_ops comments

The comments for struct v4l2_subdev_video_ops are out of the
order as the parameter would appear at struct. This is not
a problem for DocBook, but humans find harder to mentally
reorder ;)

So, put them at the right order. That makes easier to check
what's missing, and to put the comments in the right place.

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