SplitView::addItem(): add missing \since

Change-Id: I53ed6999b4d8cd4d35fd96783fe46dc94242e8f5
Reviewed-by: Caroline Chao <caroline.chao@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Christian Manning <cmanning999@gmail.com>

src/controls/SplitView.qml

@@ -166,7 +166,8 @@ Item {
     onHeightChanged: d.updateLayout()
     onOrientationChanged: d.changeOrientation()
 
-    /*! Add an item to the end of the view. */
+    /*! Add an item to the end of the view.
+        \since QtQuick.Controls 1.3 */
     function addItem(item) {
         d.updateLayoutGuard = true