s390/pci: use kmem_cache_zalloc instead of kmem_cache_alloc/memset

Using kmem_cache_zalloc() instead of kmem_cache_alloc() and memset().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>