avcodec/cdxl: Mark decoder as init-threadsafe

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/cdxl.c

@@ -335,4 +335,5 @@ AVCodec ff_cdxl_decoder = {
     .close          = cdxl_decode_end,
     .decode         = cdxl_decode_frame,
     .capabilities   = AV_CODEC_CAP_DR1,
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };