avcodec/libschroedingerenc: add missing AVClass to private context

Fixes ticket #5104.

libavcodec/libschroedingerenc.c

@@ -44,6 +44,8 @@
 
 /** libschroedinger encoder private data */
 typedef struct SchroEncoderParams {
+    AVClass        *class;
+
     /** Schroedinger video format */
     SchroVideoFormat *format;