[llvm] [AMDGPU] Fix negative immediate offset for unbuffered smem loads (PR #79553)

[Matt Arsenault via llvm-commits]

================
@@ -2169,6 +2198,11 @@ bool AMDGPUDAGToDAGISel::SelectSMRDBufferSgprImm(SDValue N, SDValue &SOffset,
                               /* IsBuffer */ true);
 }
 
+bool AMDGPUDAGToDAGISel::SelectSMRDPrefetchImm(SDValue Addr, SDValue &SBase,
+                                               SDValue &Offset) const {
+  return SelectSMRD(Addr, SBase, /* SOffset */ nullptr, &Offset, false, true);
----------------
arsenm wrote:

```suggestion
  return SelectSMRD(Addr, SBase, /*SOffset=*/ nullptr, &Offset, false, true);
```

https://github.com/llvm/llvm-project/pull/79553