media: rc: ensure input/lirc device can be opened after register

Since commit cb84343f ("media: lirc: do not call close() or open() on
unregistered devices") rc_open() will return -ENODEV if rcdev->registered
is false. Ensure this is set before we register the input device and the
lirc device, else we have a short window where the neither the lirc or
input device can be opened.

Fixes: cb84343f ("media: lirc: do not call close() or open() on unregistered devices")

Cc: stable@vger.kernel.org # v4.16+
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>