return an ERR_PTR from __filemap_get_folio v2

[Andrew Morton]

On Sun, 22 Jan 2023 08:20:06 +0100 Christoph Hellwig <hch at lst.de> wrote:

> On Sat, Jan 21, 2023 at 05:06:41PM -0800, Andrew Morton wrote:
> > This patchset doesn't apply to fs/btrfs/ because linux-next contains
> > this 6+ month-old commit:
> 
> Hmm.  It was literally written against linux-next as of last morning,
> which does not have that commit.

Confused.  According to 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/fs/btrfs/disk-io.c#n4023

it's there today.  wait_dev_supers() has been foliofied.