V4L/DVB (4652): Misc fixes for DiB3000MC and Nova-T 500

- make the timing frequency update work.
- fix AGC calibration for Nova-T 500

Signed-off-by: Patrick Boettcher <pb@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>