You can use a UNION statement to join two select statements into one result.
http://www.mysqltutorial.org/sql-union-mysql.aspx
However it looks like you would just need to adjust your SQL statement to include both years like:
<?php
$rsChartInfo = new WA_MySQLi_RS("rsChartInfo",$connTest,0);
$rsChartInfo->setQuery("SELECT MONTH(date_created) MONTH, COUNT(*) COUNT FROM qr_forms_info WHERE YEAR(date_created)=YEAR(CURDATE()) OR YEAR(date_created)=YEAR(CURDATE()) -1 GROUP BY MONTH(date_created)");
$rsChartInfo->execute();
?>