filemap: Add folio_next_pos()

filemap: Add folio_next_pos()

Replace the open-coded implementation in ocfs2 (which loses the top
32 bits on 32-bit architectures) with a helper in pagemap.h.

Fixes: 35edec1d52c0 (ocfs2: update truncate handling of partial clusters)
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20251024170822.1427218-2-willy@infradead.org
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: ocfs2-devel@lists.linux.dev
Signed-off-by: Christian Brauner <brauner@kernel.org>