nilfs2: move inode count and block count into root object

This moves sbi->s_inodes_count and sbi->s_blocks_count into nilfs_root
object.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 7e883d5..ca09e43 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -306,7 +306,7 @@
 		goto failed_ifile_create_inode;
 	/* reference count of i_bh inherits from nilfs_mdt_read_block() */
 
-	atomic_inc(&sbi->s_inodes_count);
+	atomic_inc(&root->inodes_count);
 	inode_init_owner(inode, dir, mode);
 	inode->i_ino = ino;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
@@ -715,7 +715,7 @@
 	end_writeback(inode);
 
 	nilfs_ifile_delete_inode(ii->i_root->ifile, inode->i_ino);
-	atomic_dec(&NILFS_SB(sb)->s_inodes_count);
+	atomic_dec(&ii->i_root->inodes_count);
 
 	nilfs_clear_inode(inode);