[media] au8522: Set the initial modulation

We need to set the initial modulation on driver setup, or else any
calls to GET_FRONTEND prior to the first SET_FRONTEND call will get
back garbage.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>