Add support for write_iops_log

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/stat.h b/stat.h
index 89766fc..68bc970 100644
--- a/stat.h
+++ b/stat.h
@@ -128,6 +128,7 @@
 	struct io_stat slat_stat[2];		/* submission latency */
 	struct io_stat lat_stat[2];		/* total latency */
 	struct io_stat bw_stat[2];		/* bandwidth stats */
+	struct io_stat iops_stat[2];		/* IOPS stats */
 
 	/*
 	 * fio system usage accounting