ACPICA: Cleanup useless memset invocations.

This patch removes unnecessary memset() invocations where
kmem_cache_zalloc() is used for allocating memory.  It also helps to
reduce source code differences between ACPICA upstream and Linux.

[rjw: Changelog]
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>