V4L/DVB (6629): zl10353: fix default adc_clock and TRL nominal rate calculation

The default adc_clock for the zl10353 is different from what was originally
thought to be the case and the TRL nominal rate formula was incorrect as a
result.  Use a better (and hopefully now correct) formula.

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