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/amcc/yucca/cmd_yucca.c b/board/amcc/yucca/cmd_yucca.c
index cde13e4..e9cd333 100644
--- a/board/amcc/yucca/cmd_yucca.c
+++ b/board/amcc/yucca/cmd_yucca.c
@@ -58,10 +58,8 @@
 	char plbClock[4];
 	char pcixClock[4];
 
-	if (argc < 3) {
-		cmd_usage(cmdtp);
-		return 1;
-	}
+	if (argc < 3)
+		return cmd_usage(cmdtp);
 
 	if (strcmp(argv[2], "prom0") == 0)
 		chip = IIC0_BOOTPROM_ADDR;