blk-throttle: use calculate_io/bytes_allowed() for throtl_trim_slice()

blk-throttle: use calculate_io/bytes_allowed() for throtl_trim_slice()

[ Upstream commit e8368b57c006dc0e02dcd8a9dc9f2060ff5476fe ]

There are no functional changes, just make the code cleaner.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230816012708.1193747-4-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: eead0056648c ("blk-throttle: consider 'carryover_ios/bytes' in throtl_trim_slice()")
Signed-off-by: Sasha Levin <sashal@kernel.org>