[media] cec: when canceling a message, don't overwrite old status info

When a pending message was canceled (e.g. due to a timeout), then the
old tx_status info was overwritten instead of ORed. The same happened
with the tx_error_cnt field. So just modify them instead of overwriting
them.

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