[media] imon: fix my egregious brown paper bag w/rdev/idev split

Somehow, I managed to screw things up when reworking the rdev/idev split
patch from David, and started trying to get ir_input_dev from idev
instead of rdev, thus resulting in button presses hanging the system.
This fixes it.

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