Fix attention computation when padding mask is not null
Author: zhipeng93
Pull request: yes

# What does this PR do?

This PR fixed two problems when using padding mask in `LlamaAttention`. In detail,
- Replace the `bfloat.min` with `float("-inf")` as the default value for the mask. 
- Transpose the non-casual mask.

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Comments:
Pinging @Rocketknight1 so he can have a look 😉 

Will do, but might be tomorrow before I get a chance!

Hey! I am working on #27114 which should fix the attention computation issue 


> Hey! I am working on #27114 which should fix the attention computation issue

Hi @ArthurZucker, I am afraid #27114 is not enough since even if you fixed the underflow/overflow issue, the attention output of flashattention and the attention module we implemented here is different. Please feel free to try the code snippet here [1].

[1] https://github.com/huggingface/transformers/pull/26421#discussion_r1368198875

Feel free to consult #27050 as I think it explains why! 🤗 

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