afs: Convert invalidatepage to invalidate_folio

afs: Convert invalidatepage to invalidate_folio

We know the page is in the page cache, not the swap cache.  If we ever
support folios larger than 2GB, afs_invalidate_dirty() will need to be
fixed, but that's a larger project.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Acked-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Tested-by: Mike Marshall <hubcap@omnibond.com> # orangefs
Tested-by: David Howells <dhowells@redhat.com> # afs