V4L/DVB (11072): au0828: advertise only NTSC-M (as opposed to all NTSC standards)

We don't now how to make any variant of NTSC work other than NTSC-M, so don't
advertise that we support the other variants.

Signed-off-by: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>