[DWARFLinker] Avoid repeated hash lookups (NFC) (#128825)

Author: kazutakahirata

llvm/lib/DWARFLinker/Parallel/DWARFLinkerImpl.cpp

@@ -891,10 +891,9 @@ void DWARFLinkerImpl::printStatistic() {
               CU->tryGetSectionDescriptor(DebugSectionKind::DebugInfo))
         AllDebugInfoSectionsSize += (*DebugInfo)->getContents().size();
 
-    SizeByObject[Context->InputDWARFFile.FileName].Input =
-        Context->OriginalDebugInfoSize;
-    SizeByObject[Context->InputDWARFFile.FileName].Output =
-        AllDebugInfoSectionsSize;
+    auto &Size = SizeByObject[Context->InputDWARFFile.FileName];
+    Size.Input = Context->OriginalDebugInfoSize;
+    Size.Output = AllDebugInfoSectionsSize;
   }
 
   // Create a vector sorted in descending order by output size.