server: fix fd leak in error case

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/server.c b/server.c
index d72835b..beee2db 100644
--- a/server.c
+++ b/server.c
@@ -1394,6 +1394,7 @@
 
 	if (listen(sk, 0) < 0) {
 		log_err("fio: listen: %s\n", strerror(errno));
+		close(sk);
 		return -1;
 	}