hugetlb: convert hugetlb_vma_maps_page() to hugetlb_vma_maps_pfn()

pte_page() is more expensive than pte_pfn() (often it's defined as
pfn_to_page(pte_pfn())), so it makes sense to do the conversion to pfn
once (by calling folio_pfn()) rather than convert the pfn to a page each
time.

While this is a very small advantage, the main motivation is removing a
reference to folio->page.

Link: https://lkml.kernel.org/r/20250226163131.3795869-1-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>