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/drivers/gpio/pca953x.c b/drivers/gpio/pca953x.c
index d1065f4..6e82bd6 100644
--- a/drivers/gpio/pca953x.c
+++ b/drivers/gpio/pca953x.c
@@ -164,8 +164,7 @@
 	if (!c || !((argc == (c->maxargs)) ||
 		(((int)c->cmd == PCA953X_CMD_DEVICE) &&
 		 (argc == (c->maxargs - 1))))) {
-		cmd_usage(cmdtp);
-		return 1;
+		return cmd_usage(cmdtp);
 	}
 
 	/* arg2 used as chip number or pin number */