The memory return by kzalloc() or kmem_cache_zalloc() has already be set
to zero, so remove useless memset(0).

spatch with a semantic match is used to found this problem.
(http://coccinelle.lip6.fr/)
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Cc: Mike Miller <mike.miller@hp.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>