afs: Make error on cell lookup failure consistent with OpenAFS

When kafs tries to look up a cell in the DNS or the local config, it will
translate a lookup failure into EDESTADDRREQ whereas OpenAFS translates it
into ENOENT.  Applications such as West expect the latter behaviour and
fail if they see the former.

This can be seen by trying to mount an unknown cell:

   # mount -t afs %example.com:cell.root /mnt
   mount: /mnt: mount(2) system call failed: Destination address required.

Fixes: 4d673da1

 ("afs: Support the AFS dynamic root")
Reported-by: Markus Suvanto <markus.suvanto@gmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216637


Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org