SQL Server 2012 database in suspect mode after upgrade from Developer to Standard Edition
SQL Server Developer Edition is functionally equal to Enterprise Edition. The error is stating you are using features that only Developer or Enterprise support, such as Table Partitioning in this case. In order to use Standard, you cannot use any Enterprise features. 

Check Features Supported by the Editions of SQL Server 2012 for more details.

One way to fix this issue would be to take the following steps:


  
  Take the database offline.
  Install a new named instance temporarily with Developer or Enterprise edition (database engine only as that is all that is needed
  for this).
  Copy the data and log files from current location to new location.
  On temporary instance, attach database and make sure you point to the copied files in the new location and not the original files. It
  should have no problems and bring the database up.
  Remove any Enterprise features from the link above. Use the following query to see what is used in that database "SELECT feature_name FROM sys.dm_db_persisted_sku_features"
  Detach database from temporary location.
  Rename original database files by appending some word (_orig as an example) to the current name.
  Move files from temporary location to same location as original files (assuming these files have same name as original files).
  Attach database to Standard instance by selecting the file you just copied
  Database should come up with no issues at this point.
  Turn off temporary SQL instance.
  After verifying everything is ok, uninstall the temporary instance.