uwb: fix device reference leaks

This subsystem consistently fails to drop the device reference taken by
class_find_device().

Note that some of these lookup functions already take a reference to the
returned data, while others claim no reference is needed (or does not
seem need one).

Fixes: 183b9b59

 ("uwb: add the UWB stack (core files)")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>