egl/wayland: Make swrast display_sync the correct queue

egl/wayland: Make swrast display_sync the correct queue

commit 03dd9a88b0be17ff0ce91e92f6902a9a85ba584a introduced per surface
queues, but the display_sync for swrast_commit_backbuffer remained on
the old queue.  This is likely to break when dispatching the correct
queue at the top of function (which can't dispatch the sync callback
we're waiting for).

The easiest known reproduction case is running weston-subsurfaces under
weston --use-pixman

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>