proc: vmcore - use kzalloc in get_new_element()

Instead of kmalloc+memset better use straight kzalloc

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>