As from commit b7e5f10bf4, weston_view_is_opaque() is called from
debug_scene_graph_cb(), which on its own represents a (different)
scope. By default, we already have a subscriber for the 'log' scope,
which will cause a harmless, yet spurious, message.
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>