Fix typo: 'seperate' -> 'separate' in mm_grounding_dino conversion sc…

[Prawal-Sharma]

…ript

• Fixed typo in convert_mm_grounding_dino_to_hf.py where 'image_seperate.weight' should be 'image_separate.weight'
• This improves code readability and consistency

What does this PR do?

Fixes # (issue)

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[github-actions]

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

run-slow: mm_grounding_dino

[Rocketknight1]

hi @Prawal-Sharma, have you confirmed that the update matches the weight name in the checkpoint? If the checkpoints use seperate, then we have to keep that!