[llvm] [DirectX][NFC] Change usage pattern *Dxil* to *DXIL* for uniformity (PR #80778)

[S. Bharadwaj Yadavalli via llvm-commits]

bharadwajy wrote:

> The title is out-of-date now. Not sure you can update it before merging, but would be good to fix it up when merging the change.

Thanks! I updated the title.

https://github.com/llvm/llvm-project/pull/80778