memcg: update maintainers

More players joined to memory cgroup developments and Johannes' great work
changed internal design of memory cgroup dramatically.  And he will do
more works.  Michal Hokko did many bug fixes and know memory cgroup very
well.  Daisuke Nishimura helped us very much but he seems busy now.
Thanks to his works.

Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: Daisuke Nishimura <[email protected]>
Cc: Balbir Singh <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

MAINTAINERS

@@ -4302,8 +4302,9 @@ F:	include/linux/mm.h
 F:	mm/
 
 MEMORY RESOURCE CONTROLLER
+M:	Johannes Weiner <[email protected]>
+M:	Michal Hocko <[email protected]>
 M:	Balbir Singh <[email protected]>
-M:	Daisuke Nishimura <[email protected]>
 M:	KAMEZAWA Hiroyuki <[email protected]>
 L:	[email protected]
 L:	[email protected]