media: cec: disable delayed work before freeing an interrupted transmit

cec_transmit_msg_fh() drops adap->lock to wait for a blocking transmit in
wait_for_completion_killable(). If that wait is interrupted by a signal,
cancel_delayed_work_sync() can run before the CEC kthread arms the reply
timeout via schedule_delayed_work(&data->work) in cec_transmit_done_ts().
The work is then armed after the cancel, and the data is freed with its
delayed_work still pending:

  ODEBUG: free active (active state 0) object: ... hint: cec_wait_timeout

Use disable_delayed_work_sync(): it cancels the work and disables it, so
the later schedule_delayed_work() becomes a no-op and the work cannot be
re-armed. The data is freed right after, so it need not be re-enabled.

Fixes: 490d84f6d73c ("media: cec: forgot to cancel delayed work")
Reported-by: syzbot+051024d603432b4ab395@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=051024d603432b4ab395
Suggested-by: Hillf Danton <hdanton@sina.com>
Cc: stable@vger.kernel.org
Signed-off-by: Biren Pandya <birenpandya@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>

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