blk-cgroup: hold queue_lock when removing blkg->q_node

In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: hold queue_lock when removing blkg->q_node When blkg is removed from q->blkg_list from blkg_free_workfn(), queue_lock has to be held, otherwise, all kinds of bugs(list corruption, hard lockup, ..) can be triggered from blkg_destroy_all().