Standardize command usage messages with cmd_usage()

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/common/cmd_usb.c b/common/cmd_usb.c
index 8b19240..46d6eea 100644
--- a/common/cmd_usb.c
+++ b/common/cmd_usb.c
@@ -366,7 +366,7 @@
 		boot_device = argv[2];
 		break;
 	default:
-		printf("Usage:\n%s\n", cmdtp->usage);
+		cmd_usage(cmdtp);
 		return 1;
 	}
 
@@ -659,7 +659,7 @@
 		return 0;
 	}
 #endif /* CONFIG_USB_STORAGE */
-	printf("Usage:\n%s\n", cmdtp->usage);
+	cmd_usage(cmdtp);
 	return 1;
 }