[media] rc-core: reuse device numbers

Before changeset d8b4b582, the remote controller device numbers
were released when the device were unregistered. That helped to maintain
some sanity, as, when USB devices are replugged, the remote controller
would get the same number.

Restore the same behaviour.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>