mm/writeback: update filemap_dirty_folio() comment

Change to use new address space operation dirty_folio().

Link: https://lkml.kernel.org/r/20230917-trycontrib1-v1-1-db22630b8839@gmail.com


Fixes: 6f31a5a2 ("fs: Add aops->dirty_folio")
Signed-off-by: Jianguo Bau <roidinev@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>