V4L/DVB (6630): zl10353: calculate input frequency register instead of using hardcoded value

Now we know the zl10353's correct ADC clock, we can calculate the input
frequency registers correctly instead of just blindly setting them.

Signed-off-by: Chris Pascoe <c.pascoe@itee.uq.edu.au>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>