drm/amd/display: update link type to mst before topology discovery

[Description]
link type is not updated before mst topology discovery.
This causes issue when branch device response to link address after before
the start topology discovery event finishes.

[Solution]
update link type to mst before topology discovery

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>