Fix warning about comparing an enum to an integer

Change-Id: I2a35fa58c5e68d3bd2bb38599ddcf7c4e8e0deb2
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

plugins/autotest/testtreeitem.cpp

@@ -73,7 +73,7 @@ static QIcon testTreeIcon(TestTreeItem::Type type)
         QIcon(QLatin1String(":/images/func.png")),
         QIcon(QLatin1String(":/images/data.png"))
     };
-    if (type >= sizeof(icons))
+    if (static_cast<unsigned long>(type) >= sizeof(icons))
         return icons[2];
     return icons[type];
 }