drm/amd/display: Remove get_connector_for_link.

We can keep a 1:1 relation between a link and a physical
connector and hence skip the iteration. This function
is used in context of only physical connetors.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>