murmur3: fix memleak

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/murmur3.c

@@ -175,6 +175,7 @@ int main(void)
     av_murmur3_update(ctx, hashes, 256 * 16);
     av_murmur3_final(ctx, hash_result);
     av_free(hashes);
+    av_freep(&ctx);
     printf("result: 0x%"PRIx64" 0x%"PRIx64"\n", AV_RL64(hash_result), AV_RL64(hash_result + 8));
     // official reference value is 32 bit
     return AV_RL32(hash_result) != 0x6384ba69;