[media] saa7134: v4l2-compliance: fix g_tuner/s_tuner

Make saa7134 driver more V4L2 compliant: return real frequency range in
g_tuner and fail in s_tuner for non-zero tuner

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>