when the nbuckets of cache device is smaller than 1024, making cache
device will trigger BUG_ON in kernel, add a condition to avoid this.
Reported-by: Nnitroxis <n@nxs.re>
Signed-off-by: NDongbo Cao <cdbdyx@163.com>
Signed-off-by: NColy Li <colyli@suse.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>