hw/s390x/css-bridge: Realize sysbus device before accessing it

qbus_new() should not be called on unrealized device.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20231019071611.98885-10-philmd@linaro.org>

hw/s390x/css-bridge.c

@@ -95,7 +95,6 @@ static const TypeInfo virtual_css_bus_info = {
 
 VirtualCssBus *virtual_css_bus_init(void)
 {
-    VirtualCssBus *cbus;
     BusState *bus;
     DeviceState *dev;
 
@@ -103,19 +102,19 @@ VirtualCssBus *virtual_css_bus_init(void)
     dev = qdev_new(TYPE_VIRTUAL_CSS_BRIDGE);
     object_property_add_child(qdev_get_machine(), TYPE_VIRTUAL_CSS_BRIDGE,
                               OBJECT(dev));
-    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
 
     /* Create bus on bridge device */
     bus = qbus_new(TYPE_VIRTUAL_CSS_BUS, dev, "virtual-css");
-    cbus = VIRTUAL_CSS_BUS(bus);
 
     /* Enable hotplugging */
     qbus_set_hotplug_handler(bus, OBJECT(dev));
 
+    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
+
     css_register_io_adapters(CSS_IO_ADAPTER_VIRTIO, true, false,
                              0, &error_abort);
 
-    return cbus;
+    return VIRTUAL_CSS_BUS(bus);
  }
 
 /***************** Virtual-css Bus Bridge Device ********************/