Use kzalloc rather than kmalloc followed by memset with 0.

Generated by: scripts/coccinelle/api/alloc/kzalloc-simple.cocci
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Adam Radford <aradford@gmail.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>