staging: comedi: me4000: 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/me4000.c

@@ -1105,7 +1105,7 @@ static irqreturn_t me4000_ai_isr(int irq, void *dev_id)
 {
 	unsigned int tmp;
 	struct comedi_device *dev = dev_id;
-	struct comedi_subdevice *s = &dev->subdevices[0];
+	struct comedi_subdevice *s = dev->read_subdev;
 	int i;
 	int c = 0;
 	unsigned int lval;