[media] cxd2820r: improve IF frequency setting

Use 64-bit calculation.

Return error if tuner does not provide get_if_frequency() callback.
All currently used tuners has it.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>