I did a SQL inplace upgrade from 2008 R2 to 2014 SP2. The SQL was dedicated to SCCM server and hosted only SCCM, WSUS and Reporting Services databases.
Upgrade was easy, but after upgrade the SQL Reports were not opening and the error was "Failed to load expressions host assembly. Details: Could not load file or assembly ‘SrsResources. Culture=Neutral’ or one of its dependencies. The system cannot find the file specified."
To solve this just reinstall the Reporting Services Point role in SCCM.
There is a workaround described here, but I think it is not supported by Microsoft.