Fix Wav2Vec2 Fairseq conversion (weight norm state dict keys)

[gau-nernst]

What does this PR do?

Close #31633

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

@sanchit-gandhi @amyeroberts

To test

wget https://dl.fbaipublicfiles.com/fairseq/wav2vec/wav2vec_small.pt  # wav2vec2-base checkpoint from facebook
pip install git+https://github.com/facebookresearch/fairseq.git  # install fairseq

python src/transformers/models/wav2vec2/convert_wav2vec2_original_pytorch_checkpoint_to_pytorch.py \
    --pytorch_dump_folder wav2vec2-base \
    --checkpoint_path wav2vec_small.pt \
    --config_path facebook/wav2vec2-base \
    --not_finetuned

I only checked for Wav2Vec2 base. Other checkpoints should work too. See other checkpoints from fairseq here: https://github.com/facebookresearch/fairseq/tree/main/examples/wav2vec

e.g. https://dl.fbaipublicfiles.com/fairseq/wav2vec/libri960_big.pt corresponds to https://huggingface.co/facebook/wav2vec2-large

[amyeroberts]

cc @kamilakesbi