avcodec/rka: use 64bit for srate_pad computation

Fixes: left shift of 538976288 by 13 places cannot be represented in type 'int'
Fixes: 56148/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_RKA_fuzzer-6257370708967424

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/rka.c

@@ -207,7 +207,7 @@ static int chctx_init(RKAContext *s, ChContext *c,
     c->bprob[0] = s->bprob[0];
     c->bprob[1] = s->bprob[1];
 
-    c->srate_pad = (sample_rate << 13) / 44100 & 0xFFFFFFFCU;
+    c->srate_pad = ((int64_t)sample_rate << 13) / 44100 & 0xFFFFFFFCU;
     c->pos_idx = 1;
 
     for (int i = 0; i < FF_ARRAY_ELEMS(s->bprob[0]); i++)