'1' is minimum value for queue depth, don't allow 0

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/options.c b/options.c
index 0fc9955..c56b9df 100644
--- a/options.c
+++ b/options.c
@@ -396,6 +396,7 @@
 		.type	= FIO_OPT_INT,
 		.off1	= td_var_offset(iodepth),
 		.help	= "Amount of IO buffers to keep in flight",
+		.minval = 1,
 		.def	= "1",
 	},
 	{