bfq fix for missing lock

Please consider backporting 181490d5321806e537dc5386db5ea640b826bf78 ("block, bfq: protect 'bfqd->queued' by 'bfqd->lock'"), which was merged in 5.19

applies cleanly to the lts trees I have (4.14 - 5.15), glancing at the git history it looks like this bug has been present since bfq was introduced in 4.14ish, so the above stables should be enough.