TF CLM example fix typo
Fixes a one-line typo in the TF CLM example - it was still using `MODEL_FOR_MASKED_LM_MAPPING`
Also oop, this looks like it was based on a slightly older branch - it won't cause any problems, but the "Files changed" tab lists some changes in other files that are already merged - the only one actually affected is `run_clm.py`<|||||>There might be more such remnants from the MLM script, see https://github.com/huggingface/transformers/pull/14014

cc @Rocketknight1 