return an ERR_PTR from __filemap_get_folio v2

[Christoph Hellwig]

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.