[media] lirc: use-after free while reading from device and unplugging

Many lirc drivers have their own receive buffers which are freed on
unplug (e.g. ir_lirc_unregister). This means that ir->buf->wait_poll
will be freed directly after unplug so do not remove yourself from the
wait queue.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>