Fix incorrect table name during catalog product indexing

The left join used an incorrect table name and it added way more rows for a single entity than it should
and the entity id wasn't unique anymore, which failed the insert part of the SQL query.

Author: Norbert Nagy

app/code/Magento/Catalog/Model/Indexer/Product/Flat/FlatTableBuilder.php

@@ -281,7 +281,7 @@ protected function _fillTemporaryFlatTable(array $tables, $storeId, $valueFieldS
             if (!empty($columnValueNames)) {
                 $select->joinLeft(
                     $temporaryValueTableName,
-                    sprintf('e.%1$s = %2$s.%1$s', $linkField, $temporaryTableName),
+                    sprintf('e.%1$s = %2$s.%1$s', $linkField, $temporaryValueTableName),
                     $columnValueNames
                 );
                 $allColumns = array_merge($allColumns, $columnValueNames);