nilfs2: get rid of bdi from nilfs object

Nilfs now can use sb->s_bdi to get backing_dev_info, so we use it
instead of ns_bdi on the nilfs object and remove ns_bdi.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 92e8c76..8e77016 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -910,6 +910,7 @@
 	struct the_nilfs *nilfs;
 	struct nilfs_sb_info *sbi;
 	struct nilfs_root *fsroot;
+	struct backing_dev_info *bdi;
 	__u64 cno;
 	int err;
 
@@ -948,7 +949,9 @@
 	sb->s_export_op = &nilfs_export_ops;
 	sb->s_root = NULL;
 	sb->s_time_gran = 1;
-	sb->s_bdi = nilfs->ns_bdi;
+
+	bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
+	sb->s_bdi = bdi ? : &default_backing_dev_info;
 
 	err = load_nilfs(nilfs, sbi);
 	if (err)