reiserfs: replace obvious uses of b_page with b_folio

These places just use b_page to get to the buffer's address_space or call
page_folio() on b_page to get a folio.

Link: https://lkml.kernel.org/r/20221215214402.3522366-12-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/fs/reiserfs/tail_conversion.c b/fs/reiserfs/tail_conversion.c
index b0ae088..2cec61a 100644
--- a/fs/reiserfs/tail_conversion.c
+++ b/fs/reiserfs/tail_conversion.c
@@ -177,7 +177,7 @@ void reiserfs_unmap_buffer(struct buffer_head *bh)
 	 * BUG() on attempt to write not mapped buffer
 	 */
 	if ((!list_empty(&bh->b_assoc_buffers) || bh->b_private) && bh->b_page) {
-		struct inode *inode = bh->b_page->mapping->host;
+		struct inode *inode = bh->b_folio->mapping->host;
 		struct reiserfs_journal *j = SB_JOURNAL(inode->i_sb);
 		spin_lock(&j->j_dirty_buffers_lock);
 		list_del_init(&bh->b_assoc_buffers);