media: cec: improve debugging

cec_transmit_msg_fh() first checked the message for errors, and only
after the message was found to be valid did it log the message contents.

However, that makes it hard to associate an error in the kernel log with
the message since the message contents was never logged in that case.

So swap the order: first log the message (once some very basic checks
are done), and only after that check for errors.

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