blk-iocost: clamp inuse and skip noops in __propagate_weights()

[ Upstream commit db84a72af6be422abf2089a5896293590dda5066 ]

__propagate_weights() currently expects the callers to clamp inuse within
[1, active], which is needlessly fragile. The inuse adjustment logic is
going to be revamped, in preparation, let's make __propagate_weights() clamp
inuse on entry.

Also, make it avoid weight updates altogether if neither active or inuse is
changed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: 57e420c84f9a ("blk-iocost: Avoid using clamp() on inuse in __propagate_weights()")
Signed-off-by: Sasha Levin <sashal@kernel.org>