[AMDGPU] Simplify emitAtomicRMWLegalRemark. NFC. (llvm#134614)

Author: jayfoad

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -16723,8 +16723,8 @@ static bool atomicIgnoresDenormalModeOrFPModeIsFTZ(const AtomicRMWInst *RMW) {
 
 static OptimizationRemark emitAtomicRMWLegalRemark(const AtomicRMWInst *RMW) {
   LLVMContext &Ctx = RMW->getContext();
-  StringRef SS = Ctx.getSyncScopeName(RMW->getSyncScopeID()).value_or("");
-  StringRef MemScope = SS.empty() ? StringRef("system") : SS;
+  StringRef MemScope =
+      Ctx.getSyncScopeName(RMW->getSyncScopeID()).value_or("system");
 
   return OptimizationRemark(DEBUG_TYPE, "Passed", RMW)
          << "Hardware instruction generated for atomic "