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>