client: fix free of wrong pointer

Signed-off-by: Hong Zhiguo <zhiguohong@tencent.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/client.c b/client.c
index b20d6dc..1fefda8 100644
--- a/client.c
+++ b/client.c
@@ -625,7 +625,7 @@
 	if (len) {
 		log_err("fio: failed reading job file %s\n", filename);
 		close(fd);
-		free(buf);
+		free(pdu);
 		return 1;
 	}