[media] cec: CEC_RECEIVE is allowed in monitor mode

When the device is in monitor mode, then you should always be able to
call CEC_RECEIVE, even it the device is unconfigured.

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