apparmor: fix error code to failure message mapping for name lookup

-ESTALE used to be incorrectly used to indicate a disconnected path, when
name lookup failed.  This was fixed in commit e1b0e444 to correctly return
-EACCESS, but the error to failure message mapping was not correctly updated
to reflect this change.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Steve Beattie <sbeattie@ubuntu.com>