drm/msm: dpu: Clear frame_busy_mask bit after trace

We're printing the frame_busy_mask in a trace, but after it's been
cleared. This, as it turns out, is pretty pointless.

Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

Signed-off-by: Rob Clark <robdclark@gmail.com>