V4L/DVB (9512): cx18: Fix write retries for registers that always change - part 3.

cx18: Fix write retries for registers that always change - part 3.
Fix the io for the rest of the registers that will often not read back the
value just written.  Modified register readback checks to make sure the
intended effect was achieved without constantly rewriting the registers.
The one outstanding register remaining is 0xc72014 CX18_AUDIO_ENABLE, whose
behavior on writes I have yet to determine.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>