More code problems detected by cppcheck

Source/core/rendering/RenderGrid.cpp

Index: Source/core/rendering/RenderGrid.cpp
diff --git a/Source/core/rendering/RenderGrid.cpp b/Source/core/rendering/RenderGrid.cpp
index 36fb8e077ab2fdc938b484214339807b3d9f0225..9d0430f862315dad71682d22f0deabff34929d4b 100644
--- a/Source/core/rendering/RenderGrid.cpp
+++ b/Source/core/rendering/RenderGrid.cpp
@@ -76,7 +76,7 @@ struct GridTrackForNormalization {
     }
 
     // Required by std::sort.
-    GridTrackForNormalization operator=(const GridTrackForNormalization& o)
+    GridTrackForNormalization& operator=(const GridTrackForNormalization& o)
     {
         m_track = o.m_track;
         m_flex = o.m_flex;