Update ext4 MAINTAINERS file

The ext4 entry was copied from ext3 and was never correct.  Update it
so that Theodore Ts'o is listed as the maintainer, and point the
website to http://ext4.wiki.kernel.org.
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

MAINTAINERS

@@ -1639,9 +1639,10 @@ L:	linux-ext4@vger.kernel.org
 S:	Maintained
 
 EXT4 FILE SYSTEM
-P:	Stephen Tweedie, Andrew Morton
-M:	sct@redhat.com, akpm@linux-foundation.org, adilger@sun.com
+P:	Theodore Ts'o
+M:	tytso@mit.edu, adilger@sun.com
 L:	linux-ext4@vger.kernel.org
+W:	http://ext4.wiki.kernel.org
 S:	Maintained
 
 F71805F HARDWARE MONITORING DRIVER