remove unnecessary bash-ism

the following patch removes unnecesary dependency on bash.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio_generate_plots b/fio_generate_plots
index 4e2cb08..ff479a7 100755
--- a/fio_generate_plots
+++ b/fio_generate_plots
@@ -1,8 +1,8 @@
-#!/bin/bash
+#! /bin/sh
 
 # Use gnuplot to generate plots from fio run with -l and/or -w
 
-if [ "$1"x == "x" ]; then
+if [ "$1"x = "x" ]; then
 	echo Need title as arg
 	exit 1
 fi