As reported by BOUWSMA Barry the readout of the signal status doesn't work
on dec3000-s models. Since we don't know how to do it better, revert back
to the old behaviour and always report a signal lock.

Reported by Barry Bouwsma
Signed-off-by: Peter Beutner <p.beutner@gmx.net>
Signed-off-by: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>