use mean instead of elementwise_mean in XLMPredLayer (#15436)

* use mean instead of elementwise_mean

* make style
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

src/transformers/models/xlm/modeling_xlm.py

@@ -659,9 +659,7 @@ class XLMPredLayer(nn.Module):
             scores = self.proj(x)
             outputs = (scores,) + outputs
             if y is not None:
-                loss = nn.functional.cross_entropy(
-                    scores.view(-1, self.n_words), y.view(-1), reduction="elementwise_mean"
-                )
+                loss = nn.functional.cross_entropy(scores.view(-1, self.n_words), y.view(-1), reduction="mean")
                 outputs = (loss,) + outputs
         else:
             scores = self.proj.log_prob(x)