The Wireless Receiver should also behave in the same way than regular
USB devices.

To simplify the unregistering of the different devices,
wacom_unregister_inputs() is introduced.
For consistency, the function wacom_register_input() is renamed into
wacom_register_inputs().
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Jason Gerecke <killertofu@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>