memcg: fix account leak at failure of memsw acconting

Commit 4b534334 ("memcg: clean up try_charge main loop") removes a
cancel of charge at case: memory charge-> success.  mem+swap charge->
failure.

This leaks usage of memory.  Fix it.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: <stable@kernel.org>	[2.6.36+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>