fix attribute access in PermuteForRope._apply

[CharlieKerfoot]

Summary

PermuteForRope._apply in src/transformers/core_model_loading.py:387 calls self.config.getattr("num_attention_heads", 1), but config objects have no getattr method, so this raises AttributeError every time the op runs.

Fix

Use the builtin getattr(self.config, "num_attention_heads", 1) to read the attribute with a default fallback, matching the original intent.

Tests

Loading a model that exercises PermuteForRope no longer raises AttributeError on the config lookup.

[Rocketknight1]

cc @ArthurZucker since it was added in #41580 - bug looks real but I think this is dead code that never gets called. Can we just remove the class?