Qualcomm AI Engine Direct - Fixed the bug in dummy_llama2 script (#2587)

Summary:
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- Add compile only argument in dummy_llama2

Pull Request resolved: https://github.com/pytorch/executorch/pull/2587

Reviewed By: kirklandsign

Differential Revision: D55248247

Pulled By: cccclai

fbshipit-source-id: cc11560b30223f425ef71391f0b43dbde25c1126