[bug] in reset method in linear.cpp

If we call reset method of nn::Linear module, we will get an error arising from nn::Module::register_parameter since we have already registered the parameter in the constructor.

We recently merged https://github.com/pytorch/pytorch/pull/29832 which adds reset_parameters() method to nn::Linear module, and it will be available in the nightly build tomorrow or in the upcoming 1.4 release.