blk-iocost: Fix typo in comment

soley -> solely

Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20221018121932.10792-2-shikemeng@huawei.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>