Redundant comparison in SoftmaxLayer<Dtype>::Forward_cpu

[csukuangfj]

Issue summary

See the code below from the master branch

    // initialize scale_data to the first plane
    caffe_copy(inner_num_, bottom_data + i * dim, scale_data);
    for (int j = 0; j < channels; j++) {
      for (int k = 0; k < inner_num_; k++) {
        scale_data[k] = std::max(scale_data[k],
            bottom_data[i * dim + j * inner_num_ + k]);
      }
    }

j should start from 1. It is useless to set j=0 to compare scale_data[k] against itself.