fw_cfg: fw_cfg is a singleton

Make sure we only have a single instance ever:
because if it isn't we can't find it so it's
useless anyway.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/nvram/fw_cfg.c

@@ -496,10 +496,9 @@ FWCfgState *fw_cfg_init(uint32_t ctl_port, uint32_t data_port,
 
     s = DO_UPCAST(FWCfgState, busdev.qdev, dev);
 
-    if (!object_resolve_path(FW_CFG_PATH, NULL)) {
-        object_property_add_child(qdev_get_machine(), FW_CFG_NAME, OBJECT(s),
-                                  NULL);
-    }
+    assert(!object_resolve_path(FW_CFG_PATH, NULL));
+
+    object_property_add_child(qdev_get_machine(), FW_CFG_NAME, OBJECT(s), NULL);
 
     qdev_init_nofail(dev);