block: Drop spurious might_sleep() from blk_put_queue()

Dan reports the following smatch detected the following:

  block/blk-cgroup.c:1863 blkcg_schedule_throttle() warn: sleeping in atomic context

caused by blkcg_schedule_throttle() calling blk_put_queue() in an
non-sleepable context.

blk_put_queue() acquired might_sleep() in 63f93fd6 ("block: mark
blk_put_queue as potentially blocking") which transferred the might_sleep()
from blk_free_queue().

blk_free_queue() acquired might_sleep() in e8c7d14a

 ("block: revert back
to synchronous request_queue removal") while turning request_queue removal
synchronous. However, this isn't necessary as nothing in the free path
actually requires sleeping.

It's pretty unusual to require a sleeping context in a put operation and
it's not needed in the first place. Let's drop it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lkml.kernel.org/r/Y7g3L6fntnTtOm63@kili
Cc: Christoph Hellwig <hch@lst.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Fixes: e8c7d14a

 ("block: revert back to synchronous request_queue removal") # v5.9+
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/Y7iFwjN+XzWvLv3y@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>