cmd_usage(): simplify return code handling

Lots of code use this construct:

	cmd_usage(cmdtp);
	return 1;

Change cmd_usage() let it return 1 - then we can replace all these
ocurrances by

	return cmd_usage(cmdtp);

This fixes a few places with incorrect return code handling, too.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/cmd_fdos.c b/common/cmd_fdos.c
index 00f7e88..a8822d9 100644
--- a/common/cmd_fdos.c
+++ b/common/cmd_fdos.c
@@ -73,8 +73,7 @@
 	name = argv [2];
 	break;
     default:
-	cmd_usage(cmdtp);
-	break;
+	return cmd_usage(cmdtp);
     }
 
     /* Init physical layer                                                   */