nilfs2: convert nilfs_page_count_clean_buffers() to take a folio

Both callers have a folio, so pass it in and use it directly.

[konishi.ryusuke@gmail.com: fixed a checkpatch warning about function declaration]
Link: https://lkml.kernel.org/r/20241002150036.1339475-3-willy@infradead.org
Link: https://lkml.kernel.org/r/20241024092602.13395-11-konishi.ryusuke@gmail.com


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>