ipalib: Make sure correct attribute name is referenced for fax
    
    Fixes the invalid attribute name reference in the
    'System: Read User Addressbook Attributes' permission.
    
    https://fedorahosted.org/freeipa/ticket/4883
    
    Reviewed-By: Martin Kosek <mkosek@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>