refine prelu

paddle/fluid/operators/prelu_op.h

@@ -38,10 +38,9 @@ class PReluKernel : public framework::OpKernel<T> {
     auto dim = x->dims();
     int index = 0;
     int i = 0;
-    int temp = 0;
     if (mode == "channel") {
+      int temp = numel / (dim[0] * dim[1]);
       for (i = 0; i < numel; i++) {
-        temp = numel / (dim[0] * dim[1]);
         index = (i / temp) % dim[1];
         o_ptr[i] = x_ptr[i] > 0 ? x_ptr[i] : alpha_ptr[index] * x_ptr[i];
       }