We were missing the callback in a couple of places. Drivers may use
the flush callback to submit batched up rendering before events (for
example, damage events) are sent out, to ensure that the rendering
has been queued when the client receives the event.
Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Keith Packard <keithp@keithp.com>