[SCSI] pm8001: potential null dereference in pm8001_dev_gone_notify()

In the original code we dereferenced "pm8001_dev" before checking if it
was null.  This patch moves the dereference inside the condition.

This was found by a static checker (smatch).  I looked, but I couldn't
tell if "pm8001_dev" dev was ever actually null.  The approach in this
patch seemed like the safest response.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jack Wang <jack_wang@usish.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/pm8001/pm8001_sas.c

@@ -885,11 +885,13 @@ static void pm8001_dev_gone_notify(struct domain_device *dev)
 	u32 tag;
 	struct pm8001_hba_info *pm8001_ha;
 	struct pm8001_device *pm8001_dev = dev->lldd_dev;
-	u32 device_id = pm8001_dev->device_id;
+
 	pm8001_ha = pm8001_find_ha_by_dev(dev);
 	spin_lock_irqsave(&pm8001_ha->lock, flags);
 	pm8001_tag_alloc(pm8001_ha, &tag);
 	if (pm8001_dev) {
+		u32 device_id = pm8001_dev->device_id;
+
 		PM8001_DISC_DBG(pm8001_ha,
 			pm8001_printk("found dev[%d:%x] is gone.\n",
 			pm8001_dev->device_id, pm8001_dev->dev_type));