kcm: Call settingsChanged when resetting if config needs save

Makes the apply button work again after clicking "revert" and
changing something.


(cherry picked from commit 730c72b4)

kcm/kcm.cpp

@@ -320,6 +320,7 @@ void KCMKScreen::load()
 
     setBackendReady(false);
     m_configNeedsSave = false;
+    settingsChanged();
     if (!screenNormalized()) {
         Q_EMIT screenNormalizedChanged();
     }