Fix the DCGAN C++ shape warning (#3188) #3567

Job	Run time
pytorch_tutorial_build_worker (1, 15, linux.g5.12xlarge.nvidia.gpu)	15m 4s
pytorch_tutorial_build_worker (2, 15, linux.g5.4xlarge.nvidia.gpu)	51m 44s
pytorch_tutorial_build_worker (3, 15, linux.g5.4xlarge.nvidia.gpu)	20m 51s
pytorch_tutorial_build_worker (4, 15, linux.g5.4xlarge.nvidia.gpu)	29m 47s
pytorch_tutorial_build_worker (5, 15, linux.g5.4xlarge.nvidia.gpu)	21m 30s
pytorch_tutorial_build_worker (6, 15, linux.g5.4xlarge.nvidia.gpu)	20m 22s
pytorch_tutorial_build_worker (7, 15, linux.4xlarge.nvidia.gpu)	21m 36s
pytorch_tutorial_build_worker (8, 15, linux.4xlarge.nvidia.gpu)	16m 42s
pytorch_tutorial_build_worker (9, 15, linux.4xlarge.nvidia.gpu)	19m 46s
pytorch_tutorial_build_worker (10, 15, linux.4xlarge.nvidia.gpu)	18m 20s
pytorch_tutorial_build_worker (11, 15, linux.4xlarge.nvidia.gpu)	17m 43s
pytorch_tutorial_build_worker (12, 15, linux.4xlarge.nvidia.gpu)	33m 11s
pytorch_tutorial_build_worker (13, 15, linux.4xlarge.nvidia.gpu)	44m 54s
pytorch_tutorial_build_worker (14, 15, linux.4xlarge.nvidia.gpu)	36m 58s
pytorch_tutorial_build_worker (15, 15, linux.4xlarge.nvidia.gpu)	9m 48s
pytorch_tutorial_build_manager	0s
	6h 18m 16s

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