mm/vmstat: remove unneeded return value

The return value of pagetypeinfo_showfree and pagetypeinfo_showblockcount
are unused now.  Remove them.

Link: https://lkml.kernel.org/r/20210715122911.15700-4-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>