staging: comedi: das1800: use dev->read_subdev

Use the dev->read_subdev that was setup in the device attach instead
of accessing the dev->subdevices array directly.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/das1800.c

@@ -644,7 +644,7 @@ static int das1800_cancel(struct comedi_device *dev, struct comedi_subdevice *s)
 static void das1800_ai_handler(struct comedi_device *dev)
 {
 	struct das1800_private *devpriv = dev->private;
-	struct comedi_subdevice *s = &dev->subdevices[0];
+	struct comedi_subdevice *s = dev->read_subdev;
 	struct comedi_async *async = s->async;
 	struct comedi_cmd *cmd = &async->cmd;
 	unsigned int status = inb(dev->iobase + DAS1800_STATUS);