[media] DocBook: update documented fields at struct dmx_demux

There are a few inconsistencies between the old documentation
that got imported into the header and the current status.

Update them, and use the proper doc-nano nomenclature for
struct artuments "@", instead of foo().

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
1 file changed