foreach($Portfolio_cat as $row_2)
{
#if ($row['cid']==$row_2['cid'])
echo '<option value = "'.$row_2->cid.'" selected>'.$row_2->cname.'</option>';
}





Попробуйте так
foreach($Portfolio_cat as $row_2){ ?>
<option <?php if ($row['cid']==$row_2['cid']){ echo selected = "selected";} ?> value = "<?= $row_2->cid ?>"><?= $row_2->cname ?></option>;
ИЛИ
foreach($Portfolio_cat as $row_2)
{
if ($row['cid']==$row_2['cid']){
$selected = 'selected = "selected"';
}else{
$selected = '';
}
echo '<option '.$selected.' value = "'.$row_2->cid.'" selected>'.$row_2->cname.'</option>';
}