drm/amd/display: Revert wait vblank on update dpp clock

drm/amd/display: Revert wait vblank on update dpp clock

[Why]
This change only fix dpp clock switch to lower case.
New solution later can fix both case, which is "dc: skip
program clock when allow seamless boot"

[How]
This reverts commit "dc: wait vblank when stream enabled
and update dpp clock"

Signed-off-by: Lewis Huang <Lewis.Huang@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Wayne Lin <waynelin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>