drm/amd/display: avoid disabling opp clk before hubp is blanked.

Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>