compositor-drm: run finish_frame when dpms is turned off in update_complete

A output repaint loop isn't scheduled beacuse the output repaint_status
is AWAITING_COMPLETION when dmps is turned off in update_complete().
Therefore, the display attached to the output is remain inactive even if
weston wakes up. By going through finish_frame, the output
repaint_status is fixed to correct status.

Signed-off-by: Tomohito Esaki <etom@igel.co.jp>