MAINTAINERS: Add Andreas Gruenbacher as a maintainer for gfs2

Add Andreas Gruenbacher as a maintainer for the gfs2 file system
and remove Steve Whitehouse.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

MAINTAINERS

@@ -5939,8 +5939,8 @@ S:	Maintained
 F:	scripts/get_maintainer.pl
 
 GFS2 FILE SYSTEM
-M:	Steven Whitehouse <swhiteho@redhat.com>
 M:	Bob Peterson <rpeterso@redhat.com>
+M:	Andreas Gruenbacher <agruenba@redhat.com>
 L:	cluster-devel@redhat.com
 W:	http://sources.redhat.com/cluster/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git