!13381 fix execution order of broadcast weight grouping

From: @gong_zi_yan
Reviewed-by: @kisnwang,@stsuteng
Signed-off-by: @stsuteng

mindspore/nn/optim/optimizer.py

@@ -583,6 +583,8 @@ class Optimizer(Cell):
         new_param_group = []
         for root in range(self.dev_num):
             ops = P.Broadcast(root)
+            if root > 0:
+                param_group[root] = F.depend(param_group[root], new_param_group[root-1])
             next_params = ops(param_group[root])
             new_param_group.append(next_params)
             for i in range(F.tuple_len(next_params)):