fix graphdriver metadata buf add MergedDir

Signed-off-by: Ngaohuatao <gaohuatao@huawei.com>

src/image/oci/storage/layer_store/graphdriver/driver.c

@@ -272,6 +272,8 @@ container_inspect_graph_driver *graphdriver_get_metadata(const char *id)
                 inspect_driver->data->device_name = util_strdup_s(metadata->values[i]);
             } else if (!strcmp(metadata->keys[i], "DeviceSize")) {
                 inspect_driver->data->device_size = util_strdup_s(metadata->values[i]);
+            } else if (!strcmp(metadata->keys[i], "MergedDir")) {
+                inspect_driver->data->merged_dir = util_strdup_s(metadata->values[i]);
             }
         }
     } else {
@@ -384,4 +386,4 @@ int graphdriver_get_layer_fs_info(const char *id, imagetool_fs_info *fs_info)
     }
 
     return g_graphdriver->ops->get_layer_fs_info(id, g_graphdriver, fs_info);
-}
\ No newline at end of file
+}