drm/amd/display: Revert Scaler HCBlank issue workaround

Workaround no longer needed.

Reviewed-by: Chris Park <Chris.Park@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>