fix pinned mem USE_CUDA=1 on host with no device (#6864)
fix pinned mem USE_CUDA=1 on host with no device (#6864)

* fix pinned mem USE_CUDA=1 on host with no device

* fix

* fix

* fix

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