MAINTAINERS: move myself from ceph "Maintainer" to "Reviewer"

Xiubo has graciously volunteered to take over for me as the Linux cephfs
client maintainer. Make it official by changing myself to be a
"Reviewer" for libceph and ceph.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: jtlayton

MAINTAINERS

@@ -4547,8 +4547,8 @@ F:	drivers/power/supply/cw2015_battery.c
 
 CEPH COMMON CODE (LIBCEPH)
 M:	Ilya Dryomov <idryomov@gmail.com>
-M:	Jeff Layton <jlayton@kernel.org>
 M:	Xiubo Li <xiubli@redhat.com>
+R:	Jeff Layton <jlayton@kernel.org>
 L:	ceph-devel@vger.kernel.org
 S:	Supported
 W:	http://ceph.com/
@@ -4558,9 +4558,9 @@ F:	include/linux/crush/
 F:	net/ceph/
 
 CEPH DISTRIBUTED FILE SYSTEM CLIENT (CEPH)
-M:	Jeff Layton <jlayton@kernel.org>
 M:	Xiubo Li <xiubli@redhat.com>
 M:	Ilya Dryomov <idryomov@gmail.com>
+R:	Jeff Layton <jlayton@kernel.org>
 L:	ceph-devel@vger.kernel.org
 S:	Supported
 W:	http://ceph.com/