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_irq.c b/common/cmd_irq.c
index 4888328..d35a43f 100644
--- a/common/cmd_irq.c
+++ b/common/cmd_irq.c
@@ -27,17 +27,14 @@
 int do_interrupts(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 
-	if (argc != 2) {
-		cmd_usage(cmdtp);
-		return 1;
-	}
+	if (argc != 2)
+		return cmd_usage(cmdtp);
 
 	/* on */
-	if (strncmp(argv[1], "on", 2) == 0) {
+	if (strncmp(argv[1], "on", 2) == 0)
 		enable_interrupts();
-	} else {
+	else
 		disable_interrupts();
-	}
 
 	return 0;
 }