dataflash mmc mux: use common cmd_usage function

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/common/cmd_dataflash_mmc_mux.c b/common/cmd_dataflash_mmc_mux.c
index de4e676..fc23ed6 100644
--- a/common/cmd_dataflash_mmc_mux.c
+++ b/common/cmd_dataflash_mmc_mux.c
@@ -41,8 +41,7 @@
 			AT91F_GetMuxStatus () ? "MMC" : "SPI");
 		return 0;
 	default:
-		printf ("Usage:\n%s\n", cmdtp->usage);
-		return 1;
+		return cmd_usage(cmdtp);
 	}
 	return 0;
 }