Merge: scsi: s390: zfcp: Ensure synchronous unit_add

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/1783

JIRA: https://issues.redhat.com/browse/RHEL-129200

```
commit 9697ca0
Author: Peter Oberparleiter <oberpar@linux.ibm.com>
Date:   Tue Jun 3 20:21:56 2025 +0200

    scsi: s390: zfcp: Ensure synchronous unit_add

    Improve the usability of the unit_add sysfs attribute by ensuring that
    the associated FCP LUN scan processing is completed synchronously.  This
    enables configuration tooling to consistently determine the end of the
    scan process to allow for serialization of follow-on actions.

    While the scan process associated with unit_add typically completes
    synchronously, it is deferred to an asynchronous background process if
    unit_add is used before initial remote port scanning has completed.  This
    occurs when unit_add is used immediately after setting the associated FCP
    device online.

    To ensure synchronous unit_add processing, wait for remote port scanning
    to complete before initiating the FCP LUN scan.

    Cc: stable@vger.kernel.org
    Reviewed-by: M Nikhil <nikh1092@linux.ibm.com>
    Reviewed-by: Nihar Panda <niharp@linux.ibm.com>
    Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
    Signed-off-by: Nihar Panda <niharp@linux.ibm.com>
    Link: https://lore.kernel.org/r/20250603182252.2287285-2-niharp@linux.ibm.com
    Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
```

Signed-off-by: Nihar Panda <niharp@linux.ibm.com>
Signed-off-by: Mete Durlu <mdurlu@redhat.com>

Approved-by: Steve Best <sbest@redhat.com>
Approved-by: Tony Camuso <tcamuso@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

drivers/s390/scsi/zfcp_sysfs.c

@@ -449,6 +449,8 @@ static ssize_t zfcp_sysfs_unit_add_store(struct device *dev,
 	if (kstrtoull(buf, 0, (unsigned long long *) &fcp_lun))
 		return -EINVAL;
 
+	flush_work(&port->rport_work);
+
 	retval = zfcp_unit_add(port, fcp_lun);
 	if (retval)
 		return retval;