null_blk: force complete for timeout request

The commit 7b11eab0 ("blk-mq: blk-mq: provide forced completion
method") exports new API to force a request to complete without error
injection.

There should be no error injection when completing a request by timeout
handler.

Otherwise, the below would hang because timeout handler is failed.

echo 100 > /sys/kernel/debug/fail_io_timeout/probability
echo 1000 > /sys/kernel/debug/fail_io_timeout/times
echo 1 > /sys/block/nullb0/io-timeout-fail
dd if=/dev/zero of=/dev/nullb0 bs=512 count=1 oflag=direct

With this patch, the timeout handler is able to complete the IO.
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk_main.c

@@ -1423,7 +1423,7 @@ static bool should_requeue_request(struct request *rq)
 static enum blk_eh_timer_return null_timeout_rq(struct request *rq, bool res)
 {
 	pr_info("rq %p timed out\n", rq);
-	blk_mq_complete_request(rq);
+	blk_mq_force_complete_rq(rq);
 	return BLK_EH_DONE;
 }