fix cuda-8.0 compile

ISSUE=4613907

git-svn-id: https://svn.baidu.com/idl/trunk/paddle@1497 1ad973e4-5ce8-4261-8a94-b56d1f490c56

paddle/cuda/include/hl_device_functions.cuh

@@ -36,6 +36,8 @@ static __inline__ __device__ double atomicAdd(double* address, double val) {
 
 }  // namespace hppl
 
+#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ < 600
 using hppl::atomicAdd;
+#endif
 
 #endif /* HL_DEVICE_FUNCTIONS_CUH_ */