Fix typo in mm_grounding_dino converter

[professoralbay]

Description

Fixed a straightforward typo in the weight initialization check within the mm_grounding_dino converter script. Changed "image_seperate.weight" to "image_separate.weight".

Code Agent Policy

I confirm that this PR is fully human-written and fixes a clear typographical error. No AI agents or automated bots were used to generate this contribution.

• This pull request fixes a typo or improves the docs.
• I speak human.

[github-actions]

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

run-slow: mm_grounding_dino

[Rocketknight1]

Did you check that the weights being converted don't also have this typo? 😅

[professoralbay]

Quick update: Just verified the checkpoints on the Hub.
The original weights indeed contain the image_seperate.weight key. To maintain backward compatibility, I am adding a fallback mechanism to the PR so it can handle both the misspelled key from existing weights and the corrected image_separate.weight key.
Tested locally with this fallback, and the model loads perfectly now. Will push the code update shortly!

[Rocketknight1]

I think that's a pretty good sign that we want to keep the typo, unfortunately!