[media] DocBook: fix awkward language and fix the documented return value

The Video Standard section contains some awkward language. It also wasn't
updated when the error code for unimplemented ioctls changed from EINVAL
to ENOTTY.

[mchehab@redhat.com: remove a misplaced footnote tag]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>