blk-throttle: correct calculation of wait time in tg_may_dispatch

blk-throttle: correct calculation of wait time in tg_may_dispatch

In C language, When executing "if (expression1 && expression2)" and
expression1 return false, the expression2 may not be executed.
For "tg_within_bps_limit(tg, bio, bps_limit, &bps_wait) &&
tg_within_iops_limit(tg, bio, iops_limit, &iops_wait))", if bps is
limited, tg_within_bps_limit will return false and
tg_within_iops_limit will not be called. So even bps and iops are
both limited, iops_wait will not be calculated and is always zero.
So wait time of iops is always ignored.

Fix this by always calling tg_within_bps_limit and tg_within_iops_limit
to get wait time for both bps and iops.

Observed that:
1. Wait time in tg_within_iops_limit/tg_within_bps_limit need always
be stored as wait argument is always passed.
2. wait time is stored to zero if iops/bps is limited otherwise non-zero
is stored.
Simpfy tg_within_iops_limit/tg_within_bps_limit by removing wait argument
and return wait time directly. Caller tg_may_dispatch checks if wait time
is zero to find if iops/bps is limited.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Kemeng Shi <shikemeng@huawei.com>
Link: https://lore.kernel.org/r/20221205115709.251489-5-shikemeng@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>