Fix lupdate-Warning in qcamera.cpp.

qcamera.cpp:183: Cannot invoke tr() like this

Change-Id: Ia8f29c02bbc4b91c6542d9ed44136094e1e8a2e1
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>

src/multimedia/camera/qcamera.cpp

@@ -180,7 +180,7 @@ void QCameraPrivate::setState(QCamera::State newState)
     unsetError();
 
     if (!control) {
-        _q_error(QCamera::ServiceMissingError, q_ptr->tr("The camera service is missing"));
+        _q_error(QCamera::ServiceMissingError, QCamera::tr("The camera service is missing"));
         return;
     }