Doc: Fixed the \image reference

An earlier commit renamed the image that was
referred but this reference was not updated.

Change-Id: Ic4b6e9d6d1e01835e53a4fd4640ae45b105898fd
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>

src/controls/doc/src/qtquickcontrols-overview.qdoc

@@ -61,7 +61,7 @@
     For an overview of the controls provided by \l{Qt Quick Controls}, you can look at
     the \l{Qt Quick Controls - Gallery}{Gallery} example.
 
-    \image qtquickcontrols-example-gallery.png
+    \image qtquickcontrols-example-gallery-osx.png
 
     \section1 Setting Up Controls from C++