staging: comedi: me4000: validate the cmd->start_arg

The cmd->start_arg should be trivially validated in Step 3 of the
(*do_cmdtest) functions. Add the necessary code.
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

@@ -918,6 +918,8 @@ static int me4000_ai_do_cmd_test(struct comedi_device *dev,
 
 	/* Step 3: check if arguments are trivially valid */
 
+	err |= cfc_check_trigger_arg_is(&cmd->start_arg, 0);
+
 	if (cmd->chanlist_len < 1) {
 		cmd->chanlist_len = 1;
 		err |= -EINVAL;