[media] tda827x: improve recection with limit frequencies

tda827x is currently taking the demod IF frequency into account while
seeking for the proper tuner range. This is wrong, as the demod IF
frequency has nothing to do with the tuner PLL.

Signed-off-by: Jose Alberto Reguero <jareguero@telefonica.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>