[src] ifdef to fix compilation failure on CUDA 8 and earlier (#3103)

Author: desh2608

src/cudamatrix/cu-device.cc

@@ -111,12 +111,14 @@ void CuDevice::Initialize() {
  CUBLAS_SAFE_CALL(cublasCreate(&cublas_handle_));
  CUBLAS_SAFE_CALL(cublasSetStream(cublas_handle_, cudaStreamPerThread));
 
+ #if CUDA_VERSION >= 9000 
  if (device_options_.use_tensor_cores) {
  // Enable tensor cores in CUBLAS
  // Note if the device does not support tensor cores this will fall back to normal math mode
  CUBLAS_SAFE_CALL(cublasSetMathMode(cublas_handle_, 
  CUBLAS_TENSOR_OP_MATH));
  }
+ #endif
 
  // Initialize the cuSPARSE library
  CUSPARSE_SAFE_CALL(cusparseCreate(&cusparse_handle_));