Changing the order by parameter when getNextPendingOperation called

Changing the order by parameter to UPDATED_TIMESTAMP.

Resolves wso2/product-iots#1539

components/device-mgt/org.wso2.carbon.device.mgt.core/src/main/java/org/wso2/carbon/device/mgt/core/operation/mgt/dao/impl/GenericOperationDAOImpl.java

@@ -860,7 +860,7 @@ public class GenericOperationDAOImpl implements OperationDAO {
                     "OPERATION_CODE, om.ID AS OM_MAPPING_ID, om.UPDATED_TIMESTAMP FROM DM_OPERATION o " +
                     "INNER JOIN (SELECT * FROM DM_ENROLMENT_OP_MAPPING dm " +
                     "WHERE dm.ENROLMENT_ID = ? AND dm.STATUS = ?) om ON o.ID = om.OPERATION_ID " +
-                    "ORDER BY o.CREATED_TIMESTAMP ASC LIMIT 1");
+                    "ORDER BY om.UPDATED_TIMESTAMP ASC LIMIT 1");
             stmt.setInt(1, enrolmentId);
             stmt.setString(2, Operation.Status.PENDING.toString());
             rs = stmt.executeQuery();