avio: fix sizeof argument

Fixes CID732284
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avio.c

@@ -396,7 +396,7 @@ int ffurl_get_multi_file_handle(URLContext *h, int **handles, int *numhandles)
     if (!h->prot->url_get_multi_file_handle) {
         if (!h->prot->url_get_file_handle)
             return AVERROR(ENOSYS);
-        *handles = av_malloc(sizeof(*handles));
+        *handles = av_malloc(sizeof(**handles));
         if (!*handles)
             return AVERROR(ENOMEM);
         *numhandles = 1;