drm/amd/display: Clear cached watermark after resume
[WHY]
Driver could skip program watermarks when resume from S0i3/S4.
[HOW]
Clear the cached one first to make sure new value gets applied.
Reviewed-by: Alvin Lee <alvin.lee2@amd.com> Reviewed-by: Roman Li <roman.li@amd.com> Signed-off-by: Charlene Liu <Charlene.Liu@amd.com> Signed-off-by: Alex Hung <alex.hung@amd.com> Tested-by: Daniel Wheeler <daniel.wheeler@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>