!8175 GPU update alexnet in modelzoo

Merge pull request !8175 from VectorSL/alexnet

model_zoo/official/cv/alexnet/train.py

@@ -76,8 +76,8 @@ if __name__ == "__main__":
                                               gradients_mean=True)
             init()
     elif device_target == "GPU":
-        init()
         if device_num > 1:
+            init()
             context.reset_auto_parallel_context()
             context.set_auto_parallel_context(device_num=device_num, parallel_mode=ParallelMode.DATA_PARALLEL,
                                               gradients_mean=True)