block, bfq: don't move oom_bfqq

Our test report a UAF:

[ 2073.019181] ==================================================================
[ 2073.019188] BUG: KASAN: use-after-free in __bfq_put_async_bfqq+0xa0/0x168
[ 2073.019191] Write of size 8 at addr ffff8000ccf64128 by task rmmod/72584
[ 2073.019192]
[ 2073.019196] CPU: 0 PID: 72584 Comm: rmmod Kdump: loaded Not tainted 4.19.90-yk #5
[ 2073.019198] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[ 2073.019200] Call trace:
[ 2073.019203]  dump_backtrace+0x0/0x310
[ 2073.019206]  show_stack+0x28/0x38
[ 2073.019210]  dump_stack+0xec/0x15c
[ 2073.019216]  print_address_description+0x68/0x2d0
[ 2073.019220]  kasan_report+0x238/0x2f0
[ 2073.019224]  __asan_store8+0x88/0xb0
[ 2073.019229]  __bfq_put_async_bfqq+0xa0/0x168
[ 2073.019233]  bfq_put_async_queues+0xbc/0x208
[ 2073.019236]  bfq_pd_offline+0x178/0x238
[ 2073.019240]  blkcg_deactivate_policy+0x1f0/0x420
[ 2073.019244]  bfq_exit_queue+0x128/0x178
[ 2073.019249]  blk_mq_exit_sched+0x12c/...