Fix: qwen2vl Position Id create_causal_mask dimension
Author: jeffrey-dot-li
Pull request: yes

# What does this PR do?

Fixes qwen2vl position id tensor for create_causal_mask. Qwen2VL uses a 3d embedding system for [time, x, y] dimensions, however `create_causal_mask` expects a 1d position id and will cause errors in this line https://github.com/huggingface/transformers/blob/0cf27916f09a1a99af55ef4f2f3e8675372f38b6/src/transformers/masking_utils.py#L709 if it is given a 3d position id. 
This just uses position_id[0] for creating the causal mask.
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Comments:
**[For maintainers]** Suggested jobs to run (before merge)

run-slow: qwen2_5_omni, qwen2_5_vl, qwen2_vl

@jeffrey-dot-li hey, any updates on this PR? Would be great to merge is soon, as it is breaking inference with FA2 for qwen-vl models

hi when can this PR be merged? really looking forward to have this fix 

I made a new PR as the current one doesn't fix packing issues (https://github.com/huggingface/transformers/pull/39447). We will merge it asap