Extra memory allocated in SoftMaxLayer

[csukuangfj]

Issue summary

Extra memory is allocated for scale_ in SoftmaxLayer.

Steps to reproduce

See the code below

  outer_num_ = bottom[0]->count(0, softmax_axis_);
  inner_num_ = bottom[0]->count(softmax_axis_ + 1);
  vector<int> scale_dims = bottom[0]->shape();
  scale_dims[softmax_axis_] = 1;
  scale_.Reshape(scale_dims);

scale_ only needs inner_num_ of bytes, but outer_num_*inner_num_ of bytes are allocated.