Use class scope to refer to static function

The call to metaObject() in the ctor may generate a warning since it
calls a virtual function during construction.

Amends be09628e15

Change-Id: I27472786b41624d582525c4260a54db61ee7ed16
Reviewed-by: Harald Sitter <sitter@kde.org>
Reviewed-by: Aleix Pol Gonzalez <aleixpol@kde.org>

src/gui/accessible/linux/dbusconnection.cpp

@@ -40,7 +40,7 @@ DBusConnection::DBusConnection(QObject *parent)
     if (!addressEnv.isEmpty()) {
         // Only connect on next loop run, connections to our enabled signal are
         // only established after the ctor returns.
-        metaObject()->invokeMethod(
+        QMetaObject::invokeMethod(
                 this,
                 [this, addressEnv] {
                     m_enabled = true;