QmlDesigner: build system fix

Change-Id: I336c7d610ddd5c614b045f4a092b3c11c1d778a5
Reviewed-on: http://codereview.qt.nokia.com/585


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@nokia.com>

src/plugins/qmldesigner/qmldesigner.pro

 TEMPLATE  = subdirs
 
-SUBDIRS   = qmldesignerplugin.pro qtquickplugin symbianplugin meegoplugin extrasplugin customstyleplugin customstyleplugin
+SUBDIRS   = qmldesignerplugin.pro qtquickplugin symbianplugin meegoplugin extrasplugin desktopplugin customstyleplugin