ext3.txt: update the links in the section "useful links" to the latest ones

In Documentation/filesystems/ext3.txt, the section "useful links"
provides two links which link to ibm developerworks articles. While
the second one can be redirected to the latest one, the first one
   http://www.ibm.com/developerworks/library/l-fs7.html
fails to be redirected.

Update the 2 links to the latest ones.
Signed-off-by: NWang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: NJan Kara <jack@suse.cz>

Documentation/filesystems/ext3.txt

@@ -218,5 +218,5 @@ kernel source:	<file:fs/ext3/>
 programs: 	http://e2fsprogs.sourceforge.net/
 		http://ext2resize.sourceforge.net
 
-useful links:	http://www.ibm.com/developerworks/library/l-fs7.html
-		http://www.ibm.com/developerworks/library/l-fs8.html
+useful links:	http://www.ibm.com/developerworks/library/l-fs7/index.html
+        http://www.ibm.com/developerworks/library/l-fs8/index.html