nvdimm/blk: 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.

Since nvdimm/blk uses devm we just need to move the devm
registration towards the end. And in hindsight, that seems
to also provide a fix given del_gendisk() should not be
called unless the disk was already added via add_disk().
The probably of that issue happening is low though, like
OOM while calling devm_add_action(), so the fix is minor.

We manually unwind in case of add_disk() failure prior
to the devm registration.
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20211103230437.1639990-5-mcgrof@kernel.orgSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvdimm/blk.c

@@ -264,7 +264,9 @@ static int nsblk_attach_disk(struct nd_namespace_blk *nsblk)
 	}
 
 	set_capacity(disk, available_disk_size >> SECTOR_SHIFT);
-	device_add_disk(dev, disk, NULL);
+	rc = device_add_disk(dev, disk, NULL);
+	if (rc)
+		goto out_before_devm_err;
 
 	/* nd_blk_release_disk() is called if this fails */
 	if (devm_add_action_or_reset(dev, nd_blk_release_disk, disk))