Fix: swap input_amplitude and target_amplitude in JukeboxLoss.forward

Fixes #8820 - input_amplitude was incorrectly computed from `target` and target_amplitude from `input`. Corrected to match semantic meaning and standard forward(input, target) convention.

Signed-off-by: Zeeshan Modi <92383127+Zeesejo@users.noreply.github.com>

Author: Zeesejo

monai/losses/spectral_loss.py

@@ -55,8 +55,8 @@ def __init__(
         self.fft_norm = fft_norm
 
     def forward(self, input: torch.Tensor, target: torch.Tensor) -> torch.Tensor:
-        input_amplitude = self._get_fft_amplitude(target)
-        target_amplitude = self._get_fft_amplitude(input)
+        input_amplitude = self._get_fft_amplitude(input)
+        target_amplitude = self._get_fft_amplitude(target)
 
         # Compute distance between amplitude of frequency components
         # See Section 3.3 from https://arxiv.org/abs/2005.00341