drm/amd/display: Properly clear SCL_*_FILTER_CONTROL on DCE6

[ Upstream commit c0aa7cf4 ]

Previously, the code would set a bit field which didn't exist
on DCE6 so it would be effectively a no-op.

Fixes: b70aaf55 ("drm/amd/display: dce_transform: add DCE6 specific macros,functions")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>