The platform_check_image() stub need to return 0 for success, otherwise
the sysupgrade will fail with:
Image check 'platform_check_image' failed.
Fixes: aa6f5f1787 ("kirkwood: use image metadata")
Signed-off-by: 尤晓杰 <yxj790222@163.com>
[reworded commit message}
Signed-off-by: Mathias Kresin <dev@kresin.me>