mm/hmm: don't abuse pte_index() in hmm_vma_handle_pmd

pte_index is an internal arch helper in various architectures, without
consistent semantics.  Open code that calculation of a PMD index based on
the virtual address instead.

Link: https://lore.kernel.org/r/20190806160554.14046-10-hch@lst.deSigned-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>

mm/hmm.c

@@ -486,7 +486,7 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk,
 	if (pmd_protnone(pmd) || fault || write_fault)
 		return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
 
-	pfn = pmd_pfn(pmd) + pte_index(addr);
+	pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
 		if (pmd_devmap(pmd)) {
 			hmm_vma_walk->pgmap = get_dev_pagemap(pfn,