Instead of returning null pointer. Matches pci_create_simple(),
isa_create_simple(), sysbus_create_simple(). It's unused since the
previous commit, but I'll put it to use again shortly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>