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

This driver only supports a cmd->start_src of TRIG_INT for ai 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: 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/cb_pcidas.c

@@ -1169,7 +1169,7 @@ static int cb_pcidas_ao_inttrig(struct comedi_device *dev,
 	struct comedi_cmd *cmd = &s->async->cmd;
 	unsigned long flags;
 
-	if (trig_num != 0)
+	if (trig_num != cmd->start_arg)
 		return -EINVAL;
 
 	/*  load up fifo */