misdn: use nonseekable_open()

The driver just sets ->llseek to NULL.  It should also clear FMODE_LSEEK to
tell the VFS that seeks are not supported.

Pointed out by Christoph Hellwig.
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/mISDN/timerdev.c

@@ -61,7 +61,7 @@ mISDN_open(struct inode *ino, struct file *filep)
 	init_waitqueue_head(&dev->wait);
 	filep->private_data = dev;
 	__module_get(THIS_MODULE);
-	return 0;
+	return nonseekable_open(ino, filep);
 }
 
 static int