[media] Sanity check when initializing DVB-S/S2 demodulator

Avoid error message:
cxd2841er_read_status_s(): invalid state 1
Always force demod to shutdown state before initializing

Signed-off-by: Abylay Ospan <aospan@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>