[media] imon: allow either proto on unknown 0xffdc

While 0xffdc devices have their IR protocol hard-coded into the firmware
of the device, we have no known way of telling what it is if we don't
have the device's config byte already in the driver. Unknown devices
default to the imon native protocol, but might actually be rc6, so we
should set the driver up such that the user can load the rc6 keytable
from userspace and still have a working device ahead of its config byte
being added to the driver.

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