[media] stv0367: Remove an unused parameter

cab_state->modulation is initialized with a wrong value:

drivers/media/dvb-frontends/stv0367.c:3000:42: warning: mixing different enum types
drivers/media/dvb-frontends/stv0367.c:3000:42:     int enum fe_modulation  versus
drivers/media/dvb-frontends/stv0367.c:3000:42:     int enum stv0367cab_mod

as it was declared as "enum stv0367cab_mod". While it could be fixed,
there's no value on it, as this is never used.

So, just remove the modulation from cab_state structure.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>