io context: fix ref counting

Commit d9c7d39
("block: prevent possible io_context->refcount overflow") mistakenly
changed atomic_inc(&ioc->nr_tasks) to atomic_long_inc(&ioc->refcount).

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/iocontext.h

@@ -92,7 +92,7 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc)
 	 * a race).
 	 */
 	if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {
-		atomic_long_inc(&ioc->refcount);
+		atomic_inc(&ioc->nr_tasks);
 		return ioc;
 	}