[media] xc5000: properly show quality register values

The quality register only has relevant data in bits 2-0, so discard the
other bits (which results in a value being printed that is consistent
with the expected 0-7 range).

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