[media] lirc_dev: stray unlock in lirc_dev_fop_poll()

We shouldn't unlock here.  I think this was a cut and paste error.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>