Fix for issue with static global variables in TensorDeviceGpu.h

m_deviceProperties and m_devicePropInitialized are defined as global statics which will define multiple copies which can cause issues if initializeDeviceProp() is called in one translation unit and then m_deviceProperties is used in a different translation unit. Added inline functions getDeviceProperties() and getDevicePropInitialized() which defines those variables as static locals and returns a reference to them. As per the C++ standard 7.1.2/4, a static local declared in an inline function always refers to the same object, so this should be safer. Credit to Sun Chenggen for this fix.

Fixes #1475 (closed)