Fix new FA2 if is_causal is passed explicitly

[Cyrilvallez]

What does this PR do?

In GPT2 we have to pass is_causal explicitly for SDPA, but it causes double occurence for FA2 as highlighted in #35380. This fixes it.
Also reverts the reshape to simple view for simplicity (even if they are technically equivalent, as reshape calls view if possible)

[Cyrilvallez]

cc @ArthurZucker, this should be included in the coming release!

[HuggingFaceDocBuilderDev]

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[ArthurZucker]

Okay thanks

[vasqu]

@Cyrilvallez not sure if view is gonna cause issues as non-contiguous tensors will result in an error (which really is the only reason to use reshape instead), i.e. calling contiguous before is safer imo.

[Cyrilvallez]

We were using 'view' without 'contiguous' before the refactors, so this should be fine!

[vasqu]

Sounds good! Was just overly cautious then :)

[Cyrilvallez]

No worries, thanks for double-checking!