nvdimm/pmem: use add_disk() error handling

Now that device_add_disk() supports returning an error, use
that. We must unwind alloc_dax() on error.

Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Luis Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/nvdimm/pmem.c

···
 	dax_write_cache(dax_dev, nvdimm_has_cache(nd_region));
 	pmem->dax_dev = dax_dev;
 
-	device_add_disk(dev, disk, pmem_attribute_groups);
+	rc = device_add_disk(dev, disk, pmem_attribute_groups);
+	if (rc)
+		goto out_cleanup_dax;
 	if (devm_add_action_or_reset(dev, pmem_release_disk, pmem))
 		return -ENOMEM;
 
···
 	if (!pmem->bb_state)
 		dev_warn(dev, "'badblocks' notification disabled\n");
 	return 0;
+
+out_cleanup_dax:
+	kill_dax(pmem->dax_dev);
+	put_dax(pmem->dax_dev);
 out:
 	blk_cleanup_disk(pmem->disk);
 	return rc;