staging: comedi: comedi_parport: use dev->read_subdev in interrupt handler

Use the dev->read_subdev to get the comedi_subdevice 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/comedi_parport.c

@@ -222,7 +222,7 @@ static int parport_intr_cancel(struct comedi_device *dev,
 static irqreturn_t parport_interrupt(int irq, void *d)
 {
 	struct comedi_device *dev = d;
-	struct comedi_subdevice *s = &dev->subdevices[3];
+	struct comedi_subdevice *s = dev->read_subdev;
 	unsigned int ctrl;
 
 	ctrl = inb(dev->iobase + PARPORT_CTRL_REG);