blk-wbt: fix has-sleeper queueing check

blk-wbt: fix has-sleeper queueing check

BugLink: https://bugs.launchpad.net/bugs/1810998
We need to do this inside the loop as well, or we can allow new
IO to supersede previous IO.

Tested-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(backported from commit c45e6a037a536530bd25781ac7c989e52deb2a63)
[mfo: backport:
 - hunk 1: s/rq_wait_inc_below(rqw/atomic_inc_below(&rqw->inflight/]
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>