Fix off-by-one in last_block()

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/io_u.c b/io_u.c
index 0ba4841..ec34878 100644
--- a/io_u.c
+++ b/io_u.c
@@ -83,7 +83,7 @@
 	if (!max_blocks)
 		return 0;
 
-	return max_blocks - 1;
+	return max_blocks;
 }
 
 /*