You are trying to define self.relu as a tensor in:
self.relu = nn.functional.relu(torch.FloatTensor(hidden_layer_size), torch.FloatTensor(output_size))     

Note that this call is most likely not, what you are trying to achieve, as the second argument would be used as the inplace argument.
Also, torch.FloatTensorwill create a new tensor in the provided shape with uninitialized memory, so I would recommend to use the factory methods, such astorch.zeros, torch.randn` etc.
The original error is later raised, since you are trying to call the tensor in:
self.relu(lstm_out.view(len(input_seq), -1))

Assuming you would like to use self.relu as a module, use self.relu = nn.ReLU().