[llvm] AMDGPU: Fix using illegal extract_subvector indexes (PR #154098)

[Matt Arsenault via llvm-commits]

arsenm wrote:

* **#154101** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/154101?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a>
* **#154100** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/154100?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a>
* **#154099** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/154099?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a>
* **#154098** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/154098?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a> 👈 <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/154098?utm_source=stack-comment-view-in-graphite" target="_blank">(View in Graphite)</a>
* `main`


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https://github.com/llvm/llvm-project/pull/154098