drm/amd/display: Don't program scaler if we have no surface

If we don't have a surface in dc_commit_streams scl_data won't get
populated in resource_build_scaling_params_for_context. In this case we
shouldn't attempt to program the scaler.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>