V4L/DVB: cx23885: Check register errors

Fix kernel Oops when number of NetUP Dual DVB-S2-CI cards more than
DVB_MAX_ADAPTERS limit.

[mchehab@redhat.com: move the return to the proper place]
Signed-off-by: Abylay Ospan <aospan@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>