nilfs2: use nilfs_btnode_create_block function

This displaces nilfs_btnode_get() use to create new btree node block
with nilfs_btnode_create_block.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/btnode.c

@@ -270,12 +270,13 @@ int nilfs_btnode_prepare_change_key(struct address_space *btnc,
 		unlock_page(obh->b_page);
 	}
 
-	err = nilfs_btnode_get(btnc, newkey, 0, &nbh, 1);
-	if (likely(!err)) {
-		BUG_ON(nbh == obh);
-		ctxt->newbh = nbh;
-	}
-	return err;
+	nbh = nilfs_btnode_create_block(btnc, newkey);
+	if (!nbh)
+		return -ENOMEM;
+
+	BUG_ON(nbh == obh);
+	ctxt->newbh = nbh;
+	return 0;
 
  failed_unlock:
 	unlock_page(obh->b_page);

fs/nilfs2/btree.c

@@ -122,12 +122,15 @@ static int nilfs_btree_get_new_block(const struct nilfs_btree *btree,
 {
 	struct address_space *btnc =
 		&NILFS_BMAP_I((struct nilfs_bmap *)btree)->i_btnode_cache;
-	int ret;
+	struct buffer_head *bh;
 
-	ret = nilfs_btnode_get(btnc, ptr, 0, bhp, 1);
-	if (!ret)
-		set_buffer_nilfs_volatile(*bhp);
-	return ret;
+	bh = nilfs_btnode_create_block(btnc, ptr);
+	if (!bh)
+		return -ENOMEM;
+
+	set_buffer_nilfs_volatile(bh);
+	*bhp = bh;
+	return 0;
 }
 
 static inline int