cbs: Ensure that reference fields always follow the associated pointer

Having these together allows us to find both pointers given the address
of only one of them.

libavcodec/cbs_jpeg.h

@@ -80,8 +80,8 @@ typedef struct JPEGRawScanHeader {
 typedef struct JPEGRawScan {
     JPEGRawScanHeader header;
     uint8_t          *data;
-    size_t            data_size;
     AVBufferRef      *data_ref;
+    size_t            data_size;
 } JPEGRawScan;
 
 typedef struct JPEGRawQuantisationTable {