[media] imon: fix initial panel key repeat suppression

As pointed out on the lirc list by Andreas Dick, initial panel key
repeat suppression wasn't working, as we had no timevals accumulated
until after the first repeat. Also add a missing locking call.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>