staging: comedi: quatech_daqp_cs: ao subdevice does not support commands

The analog output subdevice does not support aynchronous commands.
Don't set the dev->write_subdev to this subdevice.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/quatech_daqp_cs.c

@@ -763,7 +763,6 @@ static int daqp_auto_attach(struct comedi_device *dev,
 	s->cancel	= daqp_ai_cancel;
 
 	s = &dev->subdevices[1];
-	dev->write_subdev = s;
 	s->private	= local;
 	s->type		= COMEDI_SUBD_AO;
 	s->subdev_flags	= SDF_WRITEABLE;