V4L/DVB (10403): saa7134-alsa: saa7130 doesn't support digital audio

According with saa7130 public datasheet, saa7130 doesn't support
digital audio. This is also confirmed by experimental tests. So, it
doesn't make sense to let saa7134-alsa register for those chipsets.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>