fix dtype when init HF model from config

[akoumpa]

What does this PR do ?

Use config's default dtype, otherwise fall-back to default_dtype constructor param value.

Collection: [Note which collection this PR will affect]

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[github-actions]

beep boop 🤖: 🙏 The following files have warnings. In case you are familiar with these, please try helping us to improve the code base.

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Your code was analyzed with PyLint. The following annotations have been identified:

************* Module nemo.collections.llm.gpt.model.hf_auto_model_for_causal_lm
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:26:0: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:34:0: C0115: Missing class docstring (missing-class-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:60:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:71:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:74:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:94:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:106:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:120:4: C0116: Missing function or method docstring (missing-function-docstring)
nemo/collections/llm/gpt/model/hf_auto_model_for_causal_lm.py:131:4: C0116: Missing function or method docstring (missing-function-docstring)

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Your code has been rated at 8.78/10

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Thank you for improving NeMo's documentation!

[github-actions]

[🤖]: Hi @akoumpa 👋,

We wanted to let you know that a CICD pipeline for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g