Add definition for new implementation in cudnn_helper.h (cuda backend)

theano/sandbox/cuda/cudnn_helper.h

@@ -31,6 +31,7 @@ static inline cudnnStatus_t cudnnSetConvolutionNdDescriptor_v3(
 #if defined(CUDNN_VERSION) && CUDNN_VERSION < 4000
 
 #define CUDNN_CONVOLUTION_FWD_ALGO_FFT_TILING 5
+#define CUDNN_CONVOLUTION_BWD_FILTER_ALGO_3 3
 #define CUDNN_CONVOLUTION_BWD_DATA_ALGO_FFT_TILING 3
 
 #endif