mmaldec: initialize refcount using atomic_init()

This is how we initialize refcount in libavutil/buffer.c.

Signed-off-by: Wan-Teh Chang <wtc@google.com>
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavcodec/mmaldec.c

@@ -281,7 +281,7 @@ static int ffmal_update_format(AVCodecContext *avctx)
         ret = AVERROR(ENOMEM);
         goto fail;
     }
-    atomic_store(&ctx->pool_out->refcount, 1);
+    atomic_init(&ctx->pool_out->refcount, 1);
 
     if (!format_out)
         goto fail;