linux-next: build failure after merge of the xen-tip tree

[Oleksandr Andrushchenko]

> From: Stephen Rothwell <sfr at canb.auug.org.au>
> Date: Mon, 30 Jul 2018 15:08:21 +1000
> Subject: [PATCH] xen/gntdev: fix up for attach callback API change
>
> Signed-off-by: Stephen Rothwell <sfr at canb.auug.org.au>
Thank you for your patch,
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko at epam.com>