[media] media: stv0367: fix frontend modulation initialization with FE_CAB_MOD_QAM256

It was using the wrong constant for QAM256 on get_frontend.

Signed-off-by: Maks Naumov <maksqwe1@ukr.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>