media: cec: cec_transmit_msg_fh: do sanity checks first

The code that fills in the CEC_MSG_CDC_MESSAGE physical address
is now done after the sanity checks. It also only does this if the
message length is >= 4 (i.e. there is room for the physical address).

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>