drm/amd/display: Assign link type before check dsc workaround.

[Why]
link type is not assigned before check dpia_mst_dsc_always_on conditions.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: JinZe.Xu <JinZe.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>