hw/pxb: declare pxb devices as not hot-pluggable

Prevent future issues when hotplug will work for devices
attached to pxbs.

Suggested-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci-bridge/pci_expander_bridge.c

@@ -310,6 +310,7 @@ static void pxb_dev_class_init(ObjectClass *klass, void *data)
 
     dc->desc = "PCI Expander Bridge";
     dc->props = pxb_dev_properties;
+    dc->hotpluggable = false;
     set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
 }
 
@@ -343,6 +344,7 @@ static void pxb_pcie_dev_class_init(ObjectClass *klass, void *data)
 
     dc->desc = "PCI Express Expander Bridge";
     dc->props = pxb_dev_properties;
+    dc->hotpluggable = false;
     set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
 }