drm/amd/display: use MST downstream AUX to dump DPRX CRCs

[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>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c

@@ -307,7 +307,7 @@ int amdgpu_dm_crtc_set_crc_source(struct drm_crtc *crtc, const char *src_name)
 			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");