scsi: qla2xxx: Fix crash during module load unload test

During purex packet handling the driver was incorrectly freeing a
pre-allocated structure. Fix this by skipping that entry.

System crashed with the following stack during a module unload test.

Call Trace:
	sbitmap_init_node+0x7f/0x1e0
	sbitmap_queue_init_node+0x24/0x150
	blk_mq_init_bitmaps+0x3d/0xa0
	blk_mq_init_tags+0x68/0x90
	blk_mq_alloc_map_and_rqs+0x44/0x120
	blk_mq_alloc_set_map_and_rqs+0x63/0x150
	blk_mq_alloc_tag_set+0x11b/0x230
	scsi_add_host_with_dma.cold+0x3f/0x245
	qla2x00_probe_one+0xd5a/0x1b80 [qla2xxx]

Call Trace with slub_debug and debug kernel:
	kasan_report_invalid_free+0x50/0x80
	__kasan_slab_free+0x137/0x150
	slab_free_freelist_hook+0xc6/0x190
	kfree+0xe8/0x2e0
	qla2x00_free_device+0x3bb/0x5d0 [qla2xxx]
	qla2x00_remove_one+0x668/0xcf0 [qla2xxx]

Link: https://lore.kernel.org/r/20220310092604.22950-6-njavali@marvell.com
Fixes: 62e9dd17 ("scsi: qla2xxx: Change in PUREX to handle FPIN ELS requests")
Cc: stable@vger.kernel.org
Reported-by: Marco Patalano <mpatalan@redhat.com>
Tested-by: Marco Patalano <mpatalan@redhat.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Arun Easi <aeasi@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/qla2xxx/qla_os.c

@@ -3901,6 +3901,8 @@ qla24xx_free_purex_list(struct purex_list *list)
 	spin_lock_irqsave(&list->lock, flags);
 	list_for_each_entry_safe(item, next, &list->head, list) {
 		list_del(&item->list);
+		if (item == &item->vha->default_item)
+			continue;
 		kfree(item);
 	}
 	spin_unlock_irqrestore(&list->lock, flags);