[media] au8522: fix intermittent lockup of analog video decoder

It turns up the autodetection for the video standard in the au8522 is
prone to hanging the chip until a reset is performed.  This condition is
trivial to reproduce simply by tuning to a station and then rapidly
unplugging/ replugging the coax feed.

Because we've never claimed to support anything other than NTSC-M, just
disable the video-standard autodetection logic and force it to always be
NTSC-M.

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