[IPO] Simplify code with StringMap::operator[] (NFC) (#112490)

Author: kazutakahirata

llvm/include/llvm/Transforms/IPO/SampleProfileMatcher.h

@@ -201,9 +201,7 @@ class SampleProfileMatcher {
   void UpdateWithSalvagedProfiles();
 
   LocToLocMap &getIRToProfileLocationMap(const Function &F) {
-    auto Ret = FuncMappings.try_emplace(
-        FunctionSamples::getCanonicalFnName(F.getName()), LocToLocMap());
-    return Ret.first->second;
+    return FuncMappings[FunctionSamples::getCanonicalFnName(F.getName())];
   }
   void distributeIRToProfileLocationMap();
   void distributeIRToProfileLocationMap(FunctionSamples &FS);