mm/memcontrol.c: remove redundant BUG_ON() in mem_cgroup_usage_unregister_event()

In the following code:

	if (type == _MEM)
		thresholds = &memcg->thresholds;
	else if (type == _MEMSWAP)
		thresholds = &memcg->memsw_thresholds;
	else
		BUG();

	BUG_ON(!thresholds);

The BUG_ON() seems redundant.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c200875..4dc9709 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4467,12 +4467,6 @@
 	else
 		BUG();
 
-	/*
-	 * Something went wrong if we trying to unregister a threshold
-	 * if we don't have thresholds
-	 */
-	BUG_ON(!thresholds);
-
 	if (!thresholds->primary)
 		goto unlock;