dax: Use device_unregister() in unregister_dax_mapping()

Replace an open-coded device_unregister() sequence with the helper.
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/168577283989.1672036.7777592498865470652.stgit@dwillia2-xfh.jf.intel.comReviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

drivers/dax/bus.c

@@ -657,8 +657,7 @@ static void unregister_dax_mapping(void *data)
 	dev_dax->ranges[mapping->range_id].mapping = NULL;
 	mapping->range_id = -1;
 
-	device_del(dev);
-	put_device(dev);
+	device_unregister(dev);
 }
 
 static struct dev_dax_range *get_dax_range(struct device *dev)