staging: comedi: amplc_dio200_common: fix the cmd->start_arg use

This driver supports two cmd->start_src values, TRIG_NOW and TRIG_INT. TRIG_NOW
sources should always have an arg of 0. For TRIG_INT sources, the cmd->start_arg
is actually the valid trig_num that is passed to the async (*inttrig) callback.
This driver trivially validates the arg for both sources to be 0.

Refactor the (*inttrig) so that the cmd->start_arg is used to check the trig_num
instead of the open coded value.

For aesthetics, refactor the (*do_cmd) to use if/else instead of the switch when
handling the cmd->start_src.
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/amplc_dio200_common.c

@@ -281,22 +281,18 @@ static int dio200_start_intr(struct comedi_device *dev,
 	return retval;
 }
 
-/*
- * Internal trigger function to start acquisition for an 'INTERRUPT' subdevice.
- */
-static int
-dio200_inttrig_start_intr(struct comedi_device *dev, struct comedi_subdevice *s,
-			  unsigned int trignum)
+static int dio200_inttrig_start_intr(struct comedi_device *dev,
+				     struct comedi_subdevice *s,
+				     unsigned int trig_num)
 {
-	struct dio200_subdev_intr *subpriv;
+	struct dio200_subdev_intr *subpriv = s->private;
+	struct comedi_cmd *cmd = &s->async->cmd;
 	unsigned long flags;
 	int event = 0;
 
-	if (trignum != 0)
+	if (trig_num != cmd->start_arg)
 		return -EINVAL;
 
-	subpriv = s->private;
-
 	spin_lock_irqsave(&subpriv->spinlock, flags);
 	s->async->inttrig = NULL;
 	if (subpriv->active)
@@ -528,16 +524,11 @@ static int dio200_subdev_intr_cmd(struct comedi_device *dev,
 		break;
 	}
 
-	/* Set up start of acquisition. */
-	switch (cmd->start_src) {
-	case TRIG_INT:
+	if (cmd->start_src == TRIG_INT)
 		s->async->inttrig = dio200_inttrig_start_intr;
-		break;
-	default:
-		/* TRIG_NOW */
+	else	/* TRIG_NOW */
 		event = dio200_start_intr(dev, s);
-		break;
-	}
+
 	spin_unlock_irqrestore(&subpriv->spinlock, flags);
 
 	if (event)