CMakeProjectManager: Remember the preferNinja setting

There was a problem in the CMakeSettingsPage that prevented
the preferNinja setting to be remembered. This patch fixes
it.

Task-number: QTCREATORBUG-15162
Change-Id: I9ffaa67e05f2c99b5e9136f3c98004c68d03dede
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>

src/plugins/cmakeprojectmanager/cmakesettingspage.cpp

@@ -562,7 +562,7 @@ void CMakeSettingsPage::apply()
 {
     QTC_ASSERT(m_widget, return);
     m_widget->m_itemConfigWidget->store();
-    m_widget->m_model.apply();
+    m_widget->apply();
 }
 
 void CMakeSettingsPage::finish()