add fallback case for ocl convolution

The ocl convolution doesn't support tensorflow padMode well.
Add fallback check if we meet this situation, it could fix the
tensorflow MobileNet SSD failure.

Signed-off-by: Li Peng <peng.li@intel.com>

modules/dnn/src/layers/convolution_layer.cpp

@@ -759,6 +759,13 @@ public:
         for (int i = 0; i < inputs.size(); ++i)
             CV_Assert(inputs[i].u != outputs[0].u);
 
+        int inpH = inputs[0].size[2];
+        int inpW = inputs[0].size[3];
+        int out_h = (inpH + 2 * pad.height - (dilation.height * (kernel.height - 1) + 1)) / stride.height + 1;
+        int out_w = (inpW + 2 * pad.width - (dilation.width * (kernel.width - 1) + 1)) / stride.width + 1;
+        if (out_h != outputs[0].size[2] || out_w != outputs[0].size[3])
+            return false;
+
         int group = inputs[0].size[1] / umat_blobs[0].size[1];
 
         if (convolutionOp.empty())