powerpc/pci/rpadlpar: Fix device reference leaks

powerpc/pci/rpadlpar: Fix device reference leaks

BugLink: http://bugs.launchpad.net/bugs/1655969
commit 99e5cde5eae78bef95bfe7c16ccda87fb070149b upstream.

Make sure to drop any device reference taken by vio_find_node() when
adding and removing virtual I/O slots.

Fixes: 5eeb8c63a38f ("[PATCH] PCI Hotplug: rpaphp: Move VIO registration")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>