stress_cd: Cleanup

From 35bf35d4098284f26b641fb0cd0a9524b1d98627 Mon Sep 17 00:00:00 2001
From: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Date: Wed, 12 Nov 2014 13:59:52 +0800
Subject: [PATCH] stress_cd: Cleanup

* Delete some useless commtents.

* Add 'static' before functions and global variables.

* In 'read_data()' the second variable is local and it would not change after
  'read_data()' is over. Defined it as a pointer.

* Remove 'return' that follows 'pthread_exit()'.

* Add branch 'read() returndd 0' that indicates end of file.

* Merge 'syserror()' and 'error()'.

* Some cleanup.

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>