mm/memcontrol.c: suppress uninitialized-var warning with older gcc's

mm/memcontrol.c: In function 'mem_cgroup_force_empty':
mm/memcontrol.c:2280: warning: 'flags' may be used uninitialized in this function

It's a false positive.

Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -2334,7 +2334,7 @@ static int mem_cgroup_move_parent(struct page *page,
 	struct cgroup *pcg = cg->parent;
 	struct mem_cgroup *parent;
 	unsigned int nr_pages;
-	unsigned long flags;
+	unsigned long uninitialized_var(flags);
 	int ret;
 
 	/* Is ROOT ? */