pdm: repair inventory chart report

this report got broken in 2178cbed (pdm: fix pylint messages and
enable coding style test, 2020-03-09) there's no "Base" portal type.

This report has no test coverage, but the bigger problem is that the
graph from this report is not readable.

bt5/erp5_pdm/SkinTemplateItem/portal_skins/erp5_pdm/Resource_getScaledInventoryList.py

@@ -73,7 +73,7 @@ for a in range(0, len(inventory_tuple_list)):
   data = inventory_tuple_list[a]
   return_list.append(
       portal.newContent(
-          portal_type='Base',
+          portal_type='Amount',
           temp_object=True,
           id=str(a),
           title='title %s'%(a,),