powerpc/ibmebus: Fix further device reference leaks

commit 815a7141c4d1b11610dccb7fcbb38633759824f2 upstream.

Make sure to drop any reference taken by bus_find_device() when creating
devices during init and driver registration.

Fixes: 55347cc9962f ("[POWERPC] ibmebus: Add device creation and bus probing based on of_device")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>