[media] Partly revert "[media] rc-core: allow calling rc_open with device not initialized"

This partly reverts commit 078600f5.

Due to the relocation of input_register_device() call, holding down a
button on an IR remote no longer resulted in repeated key down events.

Signed-off-by: Ole Ernst <olebowle@gmx.com>
Tested-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>