Fix TypeError: 'torch.device' object is not callable

[leminhnguyen]

As the issue #1, the line 164 in stft.py was changed to

iSTFTNet-pytorch/stft.py

Line 164 in e928a6b

window_sum = window_sum.to(inverse_transform.device()) if magnitude.is_cuda else window_sum

But inverse_transform.device() will raise the exception mentioned in the title. So it can be changed to inverse_transform.device to fix the problem.