[media] cec: fix test for unconfigured adapter in main message loop

The main message loop checks if the physical address was valid, and if
not it is assumed that the adapter had been unconfigured.

However, this check is no longer correct, instead it should check
that both adap->is_configured and adap->is_configuring are false.

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