filesystems: add missing nlink wrappers

Replace direct i_nlink updates with the respective updater function
(inc_nlink, drop_nlink, clear_nlink, inode_dec_link_count).

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/ext4/migrate.c

@@ -507,7 +507,7 @@ int ext4_ext_migrate(struct inode *inode)
 	 * Set the i_nlink to zero so it will be deleted later
 	 * when we drop inode reference.
 	 */
-	tmp_inode->i_nlink = 0;
+	clear_nlink(tmp_inode);
 
 	ext4_ext_tree_init(handle, tmp_inode);
 	ext4_orphan_add(handle, tmp_inode);