TaisyncManager: use qobject_cast instead of dynamic_cast

qobject_cast is times faster dynamic_cast for objects that
inherit QObject. also, use auto keyword to not duplicate
class names.

src/Taisync/TaisyncManager.cc

@@ -318,7 +318,7 @@ TaisyncManager::_setEnabled()
 void
 TaisyncManager::_restoreVideoSettings(Fact* setting)
 {
-    SettingsFact* pFact = dynamic_cast<SettingsFact*>(setting);
+    auto* pFact = qobject_cast<SettingsFact*>(setting);
     if(pFact) {
         pFact->setVisible(qgcApp()->toolbox()->corePlugin()->adjustSettingMetaData(VideoSettings::settingsGroup, *setting->metaData()));
     }