drm/amd/display: Check if set_blank_data_double_buffer exists before call

Not all ASIC types have this function implemented - check before
calling.
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Julian Parkin <jparkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c

@@ -721,6 +721,7 @@ static void false_optc_underflow_wa(
 		dc->hwss.wait_for_mpcc_disconnect(dc, dc->res_pool, old_pipe_ctx);
 	}
 
+	if (tg->funcs->set_blank_data_double_buffer)
 		tg->funcs->set_blank_data_double_buffer(tg, true);
 
 	if (tg->funcs->is_optc_underflow_occurred(tg) && !underflow)