nilfs2: convert nilfs_btnode_delete to use a folio

Saves six calls to compound_head().

Link: https://lkml.kernel.org/r/20231114084436.2755-18-konishi.ryusuke@gmail.comSigned-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>

fs/nilfs2/btnode.c

@@ -145,19 +145,19 @@ int nilfs_btnode_submit_block(struct address_space *btnc, __u64 blocknr,
 void nilfs_btnode_delete(struct buffer_head *bh)
 {
 	struct address_space *mapping;
-	struct page *page = bh->b_page;
-	pgoff_t index = page_index(page);
+	struct folio *folio = bh->b_folio;
+	pgoff_t index = folio->index;
 	int still_dirty;
 
-	get_page(page);
-	lock_page(page);
-	wait_on_page_writeback(page);
+	folio_get(folio);
+	folio_lock(folio);
+	folio_wait_writeback(folio);
 
 	nilfs_forget_buffer(bh);
-	still_dirty = PageDirty(page);
-	mapping = page->mapping;
-	unlock_page(page);
-	put_page(page);
+	still_dirty = folio_test_dirty(folio);
+	mapping = folio->mapping;
+	folio_unlock(folio);
+	folio_put(folio);
 
 	if (!still_dirty && mapping)
 		invalidate_inode_pages2_range(mapping, index, index);