usb: gadget: Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...))

trivial patch converting ERR_PTR(PTR_ERR()) into ERR_CAST().
No functional changes.
Signed-off-by: Duan Jiong <duanj.fnst@cn.fujitsu.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/configfs.c

@@ -557,7 +557,7 @@ static struct config_group *function_make(
 
 	fi = usb_get_function_instance(func_name);
 	if (IS_ERR(fi))
-		return ERR_PTR(PTR_ERR(fi));
+		return ERR_CAST(fi);
 
 	ret = config_item_set_name(&fi->group.cg_item, name);
 	if (ret) {