scsi: be2iscsi: Fix return value in mgmt_open_connection

mgmt_open_connection is expected to return tag not errno.

In error case, just return invalid tag 0.

Signed-off-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>