libweston-desktop/xwayland: clarify 'added' logic

Setting to a constant is much easier to read and grep for than setting to
a computed variable.

There are no functional changes.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
1 file changed