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/mpl/common/common_util.c b/board/mpl/common/common_util.c
index a3722b2..b4343d8 100644
--- a/board/mpl/common/common_util.c
+++ b/board/mpl/common/common_util.c
@@ -528,8 +528,7 @@
 		return 0;
 	}
 #endif
-	cmd_usage(cmdtp);
-	return 1;
+	return cmd_usage(cmdtp);
 }