kmem_cache_alloc/memset -> kmem_cache_zalloc

Used kmem_cache_zalloc instead of kmem_cache_alloc/memset.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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