bcache: fix I/O accounting leak in detached_dev_do_request

bcache: fix I/O accounting leak in detached_dev_do_request

When a bcache device is detached, discard requests are completed
immediately. However, the I/O accounting started in
cached_dev_make_request() is not ended, leading to 100% disk
utilization reports in iostat. Add the missing bio_end_io_acct() call.

Fixes: cafe56359144 ("bcache: A block layer cache")
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
Acked-by: Coly Li <colyli@fnnas.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>