staging: comedi: ni_65xx: 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/ni_65xx.c

@@ -427,7 +427,7 @@ static irqreturn_t ni_65xx_interrupt(int irq, void *d)
 {
 	struct comedi_device *dev = d;
 	struct ni_65xx_private *devpriv = dev->private;
-	struct comedi_subdevice *s = &dev->subdevices[2];
+	struct comedi_subdevice *s = dev->read_subdev;
 	unsigned int status;
 
 	status = readb(devpriv->mite->daq_io_addr + Change_Status);