[media] dvb-frontends/cxd2841er: immediately unfreeze regs when done

Do unfreeze_regs() directly when accessing the demod registers is done,
and don't have multiple unfreeze's on different conditions, which even
can get prone to errors.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Acked-by: Abylay Ospan <aospan@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>