[media] V4L: JPEG class documentation corrections

This patch fixes following compilation warning:
Error: no ID for constraint linkend: v4l2-jpeg-chroma-subsampling.

and adds missing JPEG control class at the Table A.58.

Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>