z3fold: simplify the zhdr initialization code in init_z3fold_page()

We can simplify the zhdr initialization by memset() the zhdr first
instead of set struct member to zero one by one.  This would also make
code more compact and clear.

Link: https://lkml.kernel.org/r/20210120085851.16159-1-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>