DPI-scale PM_SubMenuOverlap after all

This actually isn't a magic value and needs to be scaled.

This partially reverts commit be1635e2d6.

Task-number: QTBUG-41864
Change-Id: Ie03c96c8b5343386f55c3ae9b988e79f943f334e
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>

src/widgets/styles/qfusionstyle.cpp

@@ -3098,7 +3098,8 @@ int QFusionStyle::pixelMetric(PixelMetric metric, const QStyleOption *option, co
         val = 2;
         break;
     case PM_SubMenuOverlap:
-        return -1; // Do not dpi-scale because the value is magic
+        val = -1;
+        break;
     case PM_DockWidgetHandleExtent:
     case PM_SplitterWidth:
         val = 4;