resource_control: fix data race in controller

Signed-off-by: Shuning Chen <[email protected]>

client/resource_group/controller/controller.go

@@ -1248,7 +1248,7 @@ func (gc *groupCostController) onRequestWait(
 	*gc.mu.storeCounter[info.StoreID()] = *gc.mu.globalCounter
 	gc.mu.Unlock()
 
-	return delta, penalty, waitDuration, gc.meta.Priority, nil
+	return delta, penalty, waitDuration, gc.getMeta().GetPriority(), nil
 }
 
 func (gc *groupCostController) onResponse(