lavc/hapenc: Use the correct printf length modifier for size_t arguments.

Fixes the following warning:
libavcodec/hapenc.c:122:20: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 4 has type ‘size_t’ [-Wformat]

Based on a patch by Diego Biurrun.

libavcodec/hapenc.c

@@ -118,7 +118,7 @@ static int hap_compress_frame(AVCodecContext *avctx, uint8_t *dst)
         /* If there is no gain from snappy, just use the raw texture. */
         if (chunk->compressed_size >= chunk->uncompressed_size) {
             av_log(avctx, AV_LOG_VERBOSE,
-                   "Snappy buffer bigger than uncompressed (%lu >= %lu bytes).\n",
+                   "Snappy buffer bigger than uncompressed (%"SIZE_SPECIFIER" >= %"SIZE_SPECIFIER" bytes).\n",
                    chunk->compressed_size, chunk->uncompressed_size);
             memcpy(chunk_dst, chunk_src, chunk->uncompressed_size);
             chunk->compressor = HAP_COMP_NONE;