staging: comedi: dt282x: fix the ao cmd->start_arg use for TRIG_INT

This driver only supports a cmd->start_src of TRIG_INT for ao commands. The
cmd->start_arg is trivially validated to be 0. For TRIG_INT source, the
cmd->start_arg is actually the valid trig_num that is passed to the async
(*inttrig) callback.

Refactor the (*inttrig) function so that the cmd->start_arg is used to check
the trig_num instead of the open coded value.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: NIan Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/dt282x.c

@@ -878,12 +878,14 @@ static int dt282x_ao_cmdtest(struct comedi_device *dev,
 }
 
 static int dt282x_ao_inttrig(struct comedi_device *dev,
-			     struct comedi_subdevice *s, unsigned int x)
+			     struct comedi_subdevice *s,
+			     unsigned int trig_num)
 {
 	struct dt282x_private *devpriv = dev->private;
+	struct comedi_cmd *cmd = &s->async->cmd;
 	int size;
 
-	if (x != 0)
+	if (trig_num != cmd->start_src)
 		return -EINVAL;
 
 	size = cfc_read_array_from_buffer(s, devpriv->dma[0].buf,