rollback torch.norm() in spectrogram() (#747)

* Update functional.py

rollback torch.norm() in spectrogram() to v0.4.0.

* Update functional.py

comment out `spec_f = complex_norm(spec_f, power=power)`.

* fixed complex_norm() instead of spectrogram() for torch.norm() issue.

* lint
Co-authored-by: bongjin.lee <bongjin.lee@navercorp.com>
Co-authored-by: Vincent QB <vincentqb@users.noreply.github.com>

torchaudio/functional.py

@@ -485,9 +485,10 @@ def complex_norm(
     Returns:
         Tensor: Power of the normed input tensor. Shape of `(..., )`
     """
-    if power == 1.0:
-        return torch.norm(complex_tensor, 2, -1)
-    return torch.norm(complex_tensor, 2, -1).pow(power)
+
+    # Replace by torch.norm once issue is fixed
+    # https://github.com/pytorch/pytorch/issues/34279
+    return complex_tensor.pow(2.).sum(-1).pow(0.5 * power)
 
 
 def angle(