iser: set sector for ambiguous mr status errors

If for some reason we failed to query the mr status, we need to make sure
to provide sufficient information for an ambiguous error (guard error on
sector 0).

Fixes: 0a7a08ad

 ("IB/iser: Implement check_protection")
Cc: <stable@vger.kernel.org>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>