srcu structure has to be cleanup via cleanup_srcu_struct(), so fix it.

Reported-by: syzbot+4f789823c1abc5accf13@syzkaller.appspotmail.com
Fixes: 704b914f ("blk-mq: move srcu from blk_mq_hw_ctx to request_queue")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220111123401.520192-1-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>