drm/radeon/mst: fix regression in lane/link handling.

BugLink: http://bugs.launchpad.net/bugs/1580526



commit b36f7d26 upstream.

The function this used changed in
    092c96a8
    drm/radeon: fix dp link rate selection (v2)

However for MST we should just always train to the
max link/rate. Though we probably need to limit this
for future hw, in theory radeon won't support it.

This fixes my 30" monitor with MST enabled.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>