[llvm] [AMDGPU][NFC] Use `getScoreUB` for XCNT insertion. (PR #162448)

[via llvm-commits]

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@@ -1019,7 +1019,7 @@ void WaitcntBrackets::updateByEvent(WaitEventType E, MachineInstr &Inst) {
       // SMEM and VMEM operations. So there will never be
       // outstanding address translations for both SMEM and
       // VMEM at the same time.
-      setScoreLB(T, CurrScore - 1);
+      setScoreLB(T, getScoreUB(T) - 1);
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easyonaadit wrote:

I want to keep exactly one pending Xcnt event.
`UBScore` gets updated at the start of this function, if I use that as-is, it'll mark all xcnt events as completed.

https://github.com/llvm/llvm-project/pull/162448