Fix GGUF dequantize for `gguf==0.9.1`
Author: Isotr0py
Pull request: yes

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- The current transformers gguf integration dequantization doesn't fit the `gguf==0.9.1` because of the incorrect `nums_block` calculation after the package update (where `len(data) != n_bytes` anymore).
- This PR fixes the `num_blocks` calculation to make dequantization work with `gguf==0.9.1`.


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Comments:
Yes, I have tested with `gguf==0.6.0` and `gguf==0.9.1` on `test_q4_0` and `test_q6_k` tests, and the unittest passed. So I think the implementation should be OK.

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