[Bugfix] Fix idefics3 tie_word_embeddings

[Isotr0py]

Purpose

• Fix [Usage]: vLLM doesn't properly handle 'tie_word_embeddings:true' for Idefics3 models #25390
• The embed_tokens is written as wte incorrectly, but it wasn't caught before because all previously released idefics3-based models have tie_word_embeddings=False

Test Plan

Test Result

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request correctly fixes a bug in the Idefics3 model where an incorrect attribute name wte was used for tying word embeddings. The change replaces it with embed_tokens, which is the correct attribute in the underlying LlamaModel. This ensures that weight tying works as expected for Idefics3 models with tie_word_embeddings=True. The fix is accurate and necessary.

[DarkLight1337]

Thanks for fixing!