[media] saa7134: use correct array offset

Smatch complains that i can be one passed the end of the array if we
don't hit the break statement.  We should be using the "audio" here like
we do in the other places.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>