Fix the inference operation of the deformable convolutional layer.

This commit removes the malloc operation in the inference
method and adds the sigmoid kernel.

Signed-off-by: Davide Sapienza <sapienza.dav@gmail.com>

src/kernels/activation_sigmoid.cu

@@ -0,0 +1,31 @@
+#include "kernels.h"
+
+__device__ 
+__forceinline__ 
+double sigmoid (double a)
+{
+    return 1.0 / (1.0 + exp (-a));
+}
+
+
+__global__
+void activation_sigmoid(dnnType *input, dnnType *output, int size) {
+
+    int stride = gridDim.x * blockDim.x;
+    int tid = blockDim.x * blockIdx.x + threadIdx.x;
+    for (int i = tid; i < size; i += stride) {
+        output[i] = sigmoid (input[i]);
+    }
+ }
+
+
+/**
+    ELU activation function
+*/
+void activationSIGMOIDForward(dnnType* srcData, dnnType* dstData, int size, cudaStream_t stream)
+{
+    int blocks = (size+255)/256;
+    int threads = 256;
+    
+    activation_sigmoid<<<blocks, threads, 0, stream>>>(srcData, dstData, size);
+}