[SCSI] zfcp: restore refcount check on port_remove

Upstream commit f3450c7b91
"[SCSI] zfcp: Replace local reference counting with common kref"
accidentally dropped a reference count check before tearing down
zfcp_ports that are potentially in use by zfcp_units.
Even remote ports in use can be removed causing
unreachable garbage objects zfcp_ports with zfcp_units.
Thus units won't come back even after a manual port_rescan.
The kref of zfcp_port->dev.kobj is already used by the driver core.
We cannot re-use it to track the number of zfcp_units.
Re-introduce our own counter for units per port
and check on port_remove.

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: <stable@vger.kernel.org> #2.6.33+
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/s390/scsi/zfcp_def.h

@@ -205,6 +205,7 @@ struct zfcp_port {
 	struct zfcp_adapter    *adapter;       /* adapter used to access port */
 	struct list_head	unit_list;	/* head of logical unit list */
 	rwlock_t		unit_list_lock; /* unit list lock */
+	atomic_t		units;	       /* zfcp_unit count */
 	atomic_t	       status;	       /* status of this remote port */
 	u64		       wwnn;	       /* WWNN if known */
 	u64		       wwpn;	       /* WWPN */