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/board/w7o/cmd_vpd.c b/board/w7o/cmd_vpd.c
index 44d40ee..cab9881 100644
--- a/board/w7o/cmd_vpd.c
+++ b/board/w7o/cmd_vpd.c
@@ -38,10 +38,8 @@
 	uchar dev_addr = CONFIG_SYS_DEF_EEPROM_ADDR;
 
 	/* Validate usage */
-	if (argc > 2) {
-		cmd_usage(cmdtp);
-		return 1;
-	}
+	if (argc > 2)
+		return cmd_usage(cmdtp);
 
 	/* Passed in EEPROM address */
 	if (argc == 2)