QConstStringData -> QStaticStringData

The class was renamed in fed603fde5.

Change-Id: I859f318e80a739f31c2666d0e3088c62b55c5f13
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/json/qjsonvalue.cpp

@@ -400,7 +400,7 @@ QString QJsonValue::toString() const
     if (t != String)
         return QString();
     stringData->ref.ref(); // the constructor below doesn't add a ref.
-    return QString(*(const QConstStringData<1> *)stringData);
+    return QString(*(const QStaticStringData<1> *)stringData);
 }
 
 /*!