drm/amd/display: Add null check in resource_log_pipe_topology_update

[WHY]
When switching from "Extend" to "Second Display Only" we sometimes
call resource_get_otg_master_for_stream on a stream for the eDP,
which is disconnected. This leads to a null pointer dereference.

[HOW]
Added a null check in dc_resource.c/resource_log_pipe_topology_update.

CC: stable@vger.kernel.org
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Natanel Roizenman <natanel.roizenman@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2302,6 +2302,10 @@ void resource_log_pipe_topology_update(struct dc *dc, struct dc_state *state)
 
 		otg_master = resource_get_otg_master_for_stream(
 				&state->res_ctx, state->streams[stream_idx]);
+
+		if (!otg_master)
+			continue;
+
 		resource_log_pipe_for_stream(dc, state, otg_master, stream_idx);
 	}
 	if (state->phantom_stream_count > 0) {