MAINTAINERS: update XFS maintainer entry

I will no longer be maintaining XFS for SGI.  Ben Myers
(bpm@sgi.com) has agreed to be the primary maintainer
for XFS in my place.  I will continue to be able to push
commits to the SGI XFS tree if required.  As such I will
continue to be a designated XFS maintainer, but plan to
serve in more of a backup role.

Signed-off-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

MAINTAINERS

@@ -7425,7 +7425,8 @@ F:	drivers/xen/*swiotlb*
 
 XFS FILESYSTEM
 P:	Silicon Graphics Inc
-M:	Alex Elder <aelder@sgi.com>
+M:	Ben Myers <bpm@sgi.com>
+M:	Alex Elder <elder@kernel.org>
 M:	xfs-masters@oss.sgi.com
 L:	xfs@oss.sgi.com
 W:	http://oss.sgi.com/projects/xfs