spapr/pci: Correct "does not support hotplugging error messages

When dynamic-reconfiguration is off, hot plug / unplug can fail with
"Bus 'spapr-pci-host-bridge' does not support hotplugging".
spapr-pci-host-bridge is a device, not a bus.  Report the name of the
bus it provides instead: 'pci.0'.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20231031111059.3407803-2-armbru@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>

hw/ppc/spapr_pci.c

@@ -1555,7 +1555,7 @@ static void spapr_pci_pre_plug(HotplugHandler *plug_handler,
          */
         if (plugged_dev->hotplugged) {
             error_setg(errp, QERR_BUS_NO_HOTPLUG,
-                       object_get_typename(OBJECT(phb)));
+                       phb->parent_obj.bus->qbus.name);
             return;
         }
     }
@@ -1676,7 +1676,7 @@ static void spapr_pci_unplug_request(HotplugHandler *plug_handler,
 
     if (!phb->dr_enabled) {
         error_setg(errp, QERR_BUS_NO_HOTPLUG,
-                   object_get_typename(OBJECT(phb)));
+                   phb->parent_obj.bus->qbus.name);
         return;
     }