[media] cec: initiator should be the same as the destination for, poll

Poll messages that are used to allocate a logical address should
use the same initiator as the destination. Instead, it expected that
the initiator was 0xf which is not according to the standard.

This also had consequences for the message checks in cec_transmit_msg_fh
that incorrectly rejected poll messages with the same initiator and
destination.

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