huge_memory: convert unmap_page() to unmap_folio()

Remove a folio->page->folio conversion.

Link: https://lkml.kernel.org/r/20220902194653.1739778-54-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>