nilfs2: convert nilfs_btnode_submit_block to use a folio

Saves two calls to compound_head().

Link: https://lkml.kernel.org/r/20231114084436.2755-17-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

@@ -75,7 +75,7 @@ int nilfs_btnode_submit_block(struct address_space *btnc, __u64 blocknr,
 {
 	struct buffer_head *bh;
 	struct inode *inode = btnc->host;
-	struct page *page;
+	struct folio *folio;
 	int err;
 
 	bh = nilfs_grab_buffer(inode, btnc, blocknr, BIT(BH_NILFS_Node));
@@ -83,7 +83,7 @@ int nilfs_btnode_submit_block(struct address_space *btnc, __u64 blocknr,
 		return -ENOMEM;
 
 	err = -EEXIST; /* internal code */
-	page = bh->b_page;
+	folio = bh->b_folio;
 
 	if (buffer_uptodate(bh) || buffer_dirty(bh))
 		goto found;
@@ -130,8 +130,8 @@ int nilfs_btnode_submit_block(struct address_space *btnc, __u64 blocknr,
 	*pbh = bh;
 
 out_locked:
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 	return err;
 }