Staging: usbip: 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: Greg Kroah-Hartman <gregkh@suse.de>