drm/amd/display: Set wm_pending when disable stutter w/a used

drm/amd/display: Set wm_pending when disable stutter w/a used

[WHY&HOW]
When stutter is disabled prior to watermark programming due to a w/a,
wm_pending should be returned as true.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>