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_vfd.c b/common/cmd_vfd.c
index 1429d31..18c14d1 100644
--- a/common/cmd_vfd.c
+++ b/common/cmd_vfd.c
@@ -49,10 +49,8 @@
 {
 	ulong bitmap;
 
-	if (argc != 2) {
-		cmd_usage(cmdtp);
-		return 1;
-	}
+	if (argc != 2)
+		return cmd_usage(cmdtp);
 
 	if (argv[1][0] == '/') {	/* select bitmap by number */
 		bitmap = simple_strtoul(argv[1]+1, NULL, 10);