Fix undefined 'input' variable

[fullyz]

What does this PR do?

Fixes self.embed_positions(input, ...) which references undefined variable input instead of input_ids in decoder forward methods.

This was introduced during cache refactoring (#35314, #44330) where the input = input_ids local alias was removed but the input reference was not updated.

-        positions = self.embed_positions(input, past_key_values_length, position_ids=position_ids)
+        positions = self.embed_positions(input_ids, past_key_values_length, position_ids=position_ids)

Currently this works because position_ids is always provided, making the first argument to embed_positions unused.

• I confirm that this is not a pure code agent PR.

Before submitting

• This PR fixes a typo or improves the docs
• Did you read the contributor guideline?
• Was this discussed/approved via a Github issue or the forum?
• Did you make sure to update the documentation with your changes? (N/A)
• Did you write any new necessary tests?

Who can review?

@ArthurZucker @Cyrilvallez

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: bart, bigbird_pegasus, mbart, plbart, pp_formulanet

[zucchini-nlp]

we don't need to pass inputs/past-length since we already pre-computed position ids a few lines above

[Cyrilvallez]

Woww, indeed a bad typo! Thanks for fixing!