scsi: target: iscsi: Free conn_ops when zalloc_cpumask_var failed

It should not free cpumask but free conn->conn_ops when zalloc_cpumask_var
failed.

Signed-off-by: tangwenji <tang.wenji@zte.com.cn>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>