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/taihu/taihu.c b/board/amcc/taihu/taihu.c
index 1682cf7..dd2aba5 100644
--- a/board/amcc/taihu/taihu.c
+++ b/board/amcc/taihu/taihu.c
@@ -101,16 +101,12 @@
 {
 	int led_no;
 
-	if (argc != 3) {
-		cmd_usage(cmd_tp);
-		return -1;
-	}
+	if (argc != 3)
+		return cmd_usage(cmd_tp);
 
 	led_no = simple_strtoul(argv[1], NULL, 16);
-	if (led_no != 1 && led_no != 2) {
-		cmd_usage(cmd_tp);
-		return -1;
-	}
+	if (led_no != 1 && led_no != 2)
+		return cmd_usage(cmd_tp);
 
 	if (strcmp(argv[2],"off") == 0x0) {
 		if (led_no == 1)
@@ -123,8 +119,7 @@
 		else
 			gpio_write_bit(31, 0);
 	} else {
-		cmd_usage(cmd_tp);
-		return -1;
+		return cmd_usage(cmd_tp);
 	}
 
 	return 0;