mm/page_alloc: minor clean up for memmap_init_compound()

mm/page_alloc: minor clean up for memmap_init_compound()

Since commit 5232c63f46fd ("mm: Make compound_pincount always available"),
compound_pincount_ptr is stored at first tail page now.  So we should call
prep_compound_head() after the first tail page is initialized to take
advantage of the likelihood of that tail struct page being cached given
that we will read them right after in prep_compound_head().

Link: https://lkml.kernel.org/r/20220611021352.13529-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>