[why]
     In MST setup, we'd use MST downstream AUX to
     dump the DPRX CRCs from sink device.
[how]
     Assign the mst_port->aux to read DPCD registers.
Signed-off-by: David (Dingchen) Zhang <dingchen.zhang@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
                        goto cleanup;
                }
 
-               aux = &aconn->dm_dp_aux.aux;
+               aux = (aconn->port) ? &aconn->port->aux : &aconn->dm_dp_aux.aux;
 
                if (!aux) {
                        DRM_DEBUG_DRIVER("No dp aux for amd connector\n");