This was forgotten from the previous mass-conversion of adding namespace
aliases to written elements.

Change-Id: Id9b7e961c941ec3b3614e3694963c3f9ef9e46eb
Reviewed-on: https://gerrit.libreoffice.org/50595Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>