Fixes build error caused by API changes in KDE 4.10

--- nightmode.cpp
+++ nightmode.cpp
@@ -74,7 +74,7 @@
 void NightmodeEffect::paintWindow(EffectWindow *w, int mask, QRegion region, WindowPaintData &data )
 {
     if (m_active) {
-        data.brightness *= (m_brightness / 100.0);
+        data.setBrightness(data.brightness() * (m_brightness / 100.0));
 //         data.saturation *= (m_brightness / 100.0);
     }
     effects->paintWindow( w, mask, region, data );