[media] cx23885: make analog support work for HVR_1250 (cx23885 variant)

The analog support in the cx23885 driver was completely broken for the
HVR-1250.  Add the necessary code.

Note that this only implements analog for the composite and s-video
inputs. The tuner input continues to be non-functional due to a lack of
analog support in the mt2131 driver.

Validated with the following boards:

HVR-1250 (0070:7911)

Thanks to Steven Toth and Hauppauge for	loaning	me various boards to
regression test	with.

Thanks-to: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Devin Heitmueler <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>