nilfs2: get rid of NILFS_I_NILFS

This replaces all references of NILFS_I_NILFS(inode)->ns_bdev with
inode->i_sb->s_bdev and unfolds remaining uses of NILFS_I_NILFS inline
function.

Before 2.6.37, referring to a nilfs object from inodes needed a
conditional judgement, and NILFS_I_NILFS was helpful to simplify it.
But now we can simply do it by going through a super block instance
like inode->i_sb->s_fs_info.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/gcinode.c b/fs/nilfs2/gcinode.c
index 6f0d60a..6e79ac0 100644
--- a/fs/nilfs2/gcinode.c
+++ b/fs/nilfs2/gcinode.c
@@ -84,9 +84,9 @@
 		goto out;
 
 	if (pbn == 0) {
-		struct inode *dat_inode = NILFS_I_NILFS(inode)->ns_dat;
-					  /* use original dat, not gc dat. */
-		err = nilfs_dat_translate(dat_inode, vbn, &pbn);
+		struct the_nilfs *nilfs = inode->i_sb->s_fs_info;
+
+		err = nilfs_dat_translate(nilfs->ns_dat, vbn, &pbn);
 		if (unlikely(err)) { /* -EIO, -ENOMEM, -ENOENT */
 			brelse(bh);
 			goto failed;
@@ -100,7 +100,7 @@
 	}
 
 	if (!buffer_mapped(bh)) {
-		bh->b_bdev = NILFS_I_NILFS(inode)->ns_bdev;
+		bh->b_bdev = inode->i_sb->s_bdev;
 		set_buffer_mapped(bh);
 	}
 	bh->b_blocknr = pbn;