commit 
1647b9b9 "brd: add dax_operations support" introduced the allocation
and freeing of a dax_device, but the allocated dax_device is not stored
into the brd_device, so brd_del_one() will eventually operate on an
uninitialized brd->dax_dev.
Fix this by storing the allocated dax_device to brd->dax_dev.
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
 {
        struct brd_device *brd;
        struct gendisk *disk;
-#ifdef CONFIG_BLK_DEV_RAM_DAX
-       struct dax_device *dax_dev;
-#endif
+
        brd = kzalloc(sizeof(*brd), GFP_KERNEL);
        if (!brd)
                goto out;
 
 #ifdef CONFIG_BLK_DEV_RAM_DAX
        queue_flag_set_unlocked(QUEUE_FLAG_DAX, brd->brd_queue);
-       dax_dev = alloc_dax(brd, disk->disk_name, &brd_dax_ops);
-       if (!dax_dev)
+       brd->dax_dev = alloc_dax(brd, disk->disk_name, &brd_dax_ops);
+       if (!brd->dax_dev)
                goto out_free_inode;
 #endif
 
 
 #ifdef CONFIG_BLK_DEV_RAM_DAX
 out_free_inode:
-       kill_dax(dax_dev);
-       put_dax(dax_dev);
+       kill_dax(brd->dax_dev);
+       put_dax(brd->dax_dev);
 #endif
 out_free_queue:
        blk_cleanup_queue(brd->brd_queue);