V4L/DVB (3162): Some fixes at cx88 controls

- Now, default control values at cx88_cx8800_ctls are honored
- default value for contrast/saturation were changed to be
in line with available documentation for the chipset;
- Removed some bad coding at set_control;
- U/V Saturation now changes proportionally

Signed-off-by: Michael Krufky <mkrufky@m1k.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@brturbo.com.br>