dataflash mmc mux: use common cmd_usage function

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

common/cmd_dataflash_mmc_mux.c

@@ -41,8 +41,7 @@ int do_dataflash_mmc_mux (cmd_tbl_t *cmdtp, int flag, int argc, char * const arg
 			AT91F_GetMuxStatus () ? "MMC" : "SPI");
 		return 0;
 	default:
-		printf ("Usage:\n%s\n", cmdtp->usage);
-		return 1;
+		return cmd_usage(cmdtp);
 	}
 	return 0;
 }