Convert the incoming struct page to a folio.  Replaces two implicit
calls to compound_head() with one explicit call.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NTheodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20230324180129.1220691-18-willy@infradead.orgSigned-off-by: NTheodore Ts'o <tytso@mit.edu>