virtio-blk: don't lock AioContext in the completion code path

virtio-blk: don't lock AioContext in the completion code path

Nothing in the completion code path relies on the AioContext lock
anymore. Virtqueues are only accessed from one thread at any moment and
the s->rq global state is protected by its own lock now.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230914140101.1065008-4-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>