nvdimm/btt: add error handling support for add_disk()

We never checked for errors on add_disk() as this function
returned void. Now that this is fixed, use the shiny new
error handling.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20211103230437.1639990-3-mcgrof@kernel.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvdimm/btt.c

@@ -1541,7 +1541,9 @@ static int btt_blk_init(struct btt *btt)
 	}
 
 	set_capacity(btt->btt_disk, btt->nlba * btt->sector_size >> 9);
-	device_add_disk(&btt->nd_btt->dev, btt->btt_disk, NULL);
+	rc = device_add_disk(&btt->nd_btt->dev, btt->btt_disk, NULL);
+	if (rc)
+		goto out_cleanup_disk;
 
 	btt->nd_btt->size = btt->nlba * (u64)btt->sector_size;
 	nvdimm_check_and_set_ro(btt->btt_disk);