Simplify the bdi name to mirror what we are doing elsewhere, and
drop them name in favor of just using a number.  This avoids a
potentially very long bdi name.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NHans de Goede <hdegoede@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>