[WHY]
drm_writeback requires to capture exact one frame in each writeback
call.

[HOW]
frame_capture is disabled after each writeback is completed.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>