Make iodepth_batch=1 by default

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/options.c b/options.c
index d17dbb1..3de2ae6 100644
--- a/options.c
+++ b/options.c
@@ -504,6 +504,8 @@
 		.off1	= td_var_offset(iodepth_batch),
 		.help	= "Number of IO to submit in one go",
 		.parent	= "iodepth",
+		.minval	= 1,
+		.def	= "1",
 	},
 	{
 		.name	= "iodepth_low",