drm/msm: dpu: Don't set frame_busy_mask for async updates

The frame_busy mask is used in frame_done event handling, which is not
invoked for async commits. So an async commit will leave the
frame_busy mask populated after it completes and future commits will start
with the busy mask incorrect.

This showed up on disable after cursor move. I was hitting the "this should
not happen" comment in the frame event worker since frame_busy was set,
we queued the event, but there were no frames pending (since async
also doesn't set that).

Reviewed-by: Fritz Koenig <frkoenig@google.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190130163220.138637-1-sean@poorly.run


Signed-off-by: Rob Clark <robdclark@chromium.org>