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_load.c b/common/cmd_load.c
index 52ed1fa..dad0303 100644
--- a/common/cmd_load.c
+++ b/common/cmd_load.c
@@ -1102,7 +1102,7 @@
 			if (strcmp(argv[1], "on") == 0)
 				hwflow_onoff(1);
 			else
-				cmd_usage(cmdtp);
+				return cmd_usage(cmdtp);
 	}
 	printf("RTS/CTS hardware flow control: %s\n", hwflow_onoff(0) ? "on" : "off");
 	return 0;