scsi: zfcp: fix missing zfcp_port reference put on -EBUSY from port_remove

With this early return due to zfcp_unit child(ren), we don't use the
zfcp_port reference from the earlier zfcp_get_port_by_wwpn() anymore and
need to put it.
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Fixes: d99b601b ("[SCSI] zfcp: restore refcount check on port_remove")
Cc: <stable@vger.kernel.org> #3.7+
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_sysfs.c

@@ -261,6 +261,7 @@ static ssize_t zfcp_sysfs_port_remove_store(struct device *dev,
 	if (atomic_read(&port->units) > 0) {
 		retval = -EBUSY;
 		mutex_unlock(&zfcp_sysfs_port_units_mutex);
+		put_device(&port->dev); /* undo zfcp_get_port_by_wwpn() */
 		goto out;
 	}
 	/* port is about to be removed, so no more unit_add */