Fixed Makefile so a null CUDA_ARCH is treated like an unset one. (#7515)
Fixed Makefile so a null CUDA_ARCH is treated like an unset one. (#7515)


Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet