drm/amd/display: set NULL value during removal for remoteSink

In MST case during removal of remote sink its descriptor pointer wasn't freed corectly.
Signed-off-by: NLeon Elazar <leon.elazar@amd.com>
Acked-by: NHarry Wentland <Harry.Wentland@amd.com>
Reviewed-by: NTony Cheng <Tony.Cheng@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -1787,7 +1787,7 @@ void dc_link_remove_remote_sink(const struct dc_link *link, const struct dc_sink
 				dc_link->remote_sinks[i] = dc_link->remote_sinks[i+1];
 				i++;
 			}
-
+			dc_link->remote_sinks[i] = NULL;
 			dc_link->sink_count--;
 			return;
 		}