NFS: Read unlock folio on nfs_page_create_from_folio() error

The netfs conversion lost a folio_unlock() for the case where
nfs_page_create_from_folio() returns an error (usually -ENOMEM).  Restore
it.

Reported-by: David Jeffery <djeffery@redhat.com>
Cc: <stable@vger.kernel.org> # 6.4+
Fixes: 000dbe0b ("NFS: Convert buffered read paths to use netfs when fscache is enabled")
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Acked-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>