[PATCH] Update ext[23] mailing list address

The ext[23] mailing list moved from sf.net to vger.kernel.org so update
the MAINTAINERS file.

Signed-off-by: Erik Mouw <erik@harddisk-recovery.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>