nilfs2: use nilfs_btree_node_size()

Use nilfs_btree_node_size() instead of open-coding.

Link: http://lkml.kernel.org/r/1485184655-3895-2-git-send-email-konishi.ryusuke@lab.ntt.co.jp
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/btree.c

@@ -1870,7 +1870,7 @@ int nilfs_btree_convert_and_insert(struct nilfs_bmap *btree,
 		di = &dreq;
 		ni = NULL;
 	} else if ((n + 1) <= NILFS_BTREE_NODE_NCHILDREN_MAX(
-			   1 << btree->b_inode->i_blkbits)) {
+			   nilfs_btree_node_size(btree))) {
 		di = &dreq;
 		ni = &nreq;
 	} else {