target: NULL dereference on error path

During a failure in transport_add_device_to_core_hba() code, we called
destroy_workqueue(dev->tmr_wq) before ->tmr_wq was allocated which leads
to an oops.

This fixes a regression introduced in with:

commit af87729
Author: Christoph Hellwig <hch@infradead.org>
Date:   Sun Jul 8 15:58:49 2012 -0400

    target: replace the processing thread with a TMR work queue

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -1098,7 +1098,7 @@ struct se_device *transport_add_device_to_core_hba(
 	 * Setup the Asymmetric Logical Unit Assignment for struct se_device
 	 */
 	if (core_setup_alua(dev, force_pt) < 0)
-		goto out;
+		goto err_dev_list;
 
 	/*
 	 * Startup the struct se_device processing thread
@@ -1108,7 +1108,7 @@ struct se_device *transport_add_device_to_core_hba(
 	if (!dev->tmr_wq) {
 		pr_err("Unable to create tmr workqueue for %s\n",
 			dev->transport->name);
-		goto out;
+		goto err_dev_list;
 	}
 	/*
 	 * Setup work_queue for QUEUE_FULL
@@ -1126,7 +1126,7 @@ struct se_device *transport_add_device_to_core_hba(
 		if (!inquiry_prod || !inquiry_rev) {
 			pr_err("All non TCM/pSCSI plugins require"
 				" INQUIRY consts\n");
-			goto out;
+			goto err_wq;
 		}
 
 		strncpy(&dev->se_sub_dev->t10_wwn.vendor[0], "LIO-ORG", 8);
@@ -1136,9 +1136,10 @@ struct se_device *transport_add_device_to_core_hba(
 	scsi_dump_inquiry(dev);
 
 	return dev;
-out:
-	destroy_workqueue(dev->tmr_wq);
 
+err_wq:
+	destroy_workqueue(dev->tmr_wq);
+err_dev_list:
 	spin_lock(&hba->device_lock);
 	list_del(&dev->dev_list);
 	hba->dev_count--;