SecurityPkg/TcgEventLogRecordLib: Define LIBRARY_CLASS

Set LIBRARY_CLASS to TcgEventLogRecordLib instead of NULL.

The library is already consumed through TcgEventLogRecordLib DSC
mappings and INF dependencies. Defining the library class explicitly
matches its current usage and avoids build warnings.

Signed-off-by: Vishal Oliyil Kunnil <vishalo@qti.qualcomm.com>