fix bug auto loading llamatokenizer

[vxfla]

What does this PR do?

Huggingface decapoda-research/llama-7b-hf config decide the name of tokenizer LLaMATokenizer, while in transformers it is LlamaTokenizer. Unify the name as LLaMATokenizer, so that we can use AutoTokenizer to load llama tokenizer.

Fixes # (issue)

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[sgugger]

Lol no, but nice try. Maybe decapoda-research/llama-7b-hf should merge one of the multiple PRs they received that fixes the tokenizer on their side.

[HuggingFaceDocBuilderDev]

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