[media] cx23885: move CI/MAC registration to a separate function

As reported by smatch:
	drivers/media/pci/cx23885/cx23885-dvb.c:2080 dvb_register() Function too hairy.  Giving up.

This is indeed a too complex function, with lots of stuff inside.
Breaking this into two functions makes it a little bit less hairy.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>