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/devpts/inode.c

@@ -549,7 +549,7 @@ void devpts_pty_kill(struct tty_struct *tty)
 
 	dentry = d_find_alias(inode);
 
-	inode->i_nlink--;
+	drop_nlink(inode);
 	d_delete(dentry);
 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
 	dput(dentry);		/* d_find_alias above */