[media] tda10023: add support for DVB-C Annex C

The difference between Annex A and C is the roll-off factor.
Properly implement it inside the driver, using the information
provided by Andreas.

Thanks-to: Andreas Oberriter <obi@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>