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/acadia/cmd_acadia.c b/board/amcc/acadia/cmd_acadia.c
index 86f86e2..6936e51 100644
--- a/board/amcc/acadia/cmd_acadia.c
+++ b/board/amcc/acadia/cmd_acadia.c
@@ -44,10 +44,8 @@
 	u8 *buf;
 	int cpu_freq;
 
-	if (argc < 3) {
-		cmd_usage(cmdtp);
-		return 1;
-	}
+	if (argc < 3)
+		return cmd_usage(cmdtp);
 
 	cpu_freq = simple_strtol(argv[1], NULL, 10);
 	if (cpu_freq != 267) {