staging: comedi: comedi_test: trigger sources are validated in (*do_cmdtest)

The trigger sources were already validataed in the (*do_cmdtest) before the
(*do_cmd) is called. Refactor the code in waveform_ai_cmd() to remove the
final else which can never be reached.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/comedi_test.c

@@ -318,12 +318,8 @@ static int waveform_ai_cmd(struct comedi_device *dev,
 
 	if (cmd->convert_src == TRIG_NOW)
 		devpriv->convert_period = 0;
-	else if (cmd->convert_src == TRIG_TIMER)
+	else	/* TRIG_TIMER */
 		devpriv->convert_period = cmd->convert_arg / nano_per_micro;
-	else {
-		comedi_error(dev, "bug setting conversion period");
-		return -1;
-	}
 
 	do_gettimeofday(&devpriv->last);
 	devpriv->usec_current = devpriv->last.tv_usec % devpriv->usec_period;