Fix issue in AV1DecodeMultiThreadedTest

runtime error -DSANITIZE=integer in
AV1DecodeMultiThreadedTest.MD5Match/2 has been fixed.

BUG=aomedia:1967

Change-Id: I081c4afe0aefc2e48dcea5edcd4230eb6e1048be

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index 057332e..6e984c4 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -2796,7 +2796,7 @@
 static int compare_tile_buffers(const void *a, const void *b) {
   const TileJobsDec *const buf1 = (const TileJobsDec *)a;
   const TileJobsDec *const buf2 = (const TileJobsDec *)b;
-  return (int)(buf2->tile_buffer->size - buf1->tile_buffer->size);
+  return (((int)buf2->tile_buffer->size) - ((int)buf1->tile_buffer->size));
 }
 
 static void enqueue_tile_jobs(AV1Decoder *pbi, AV1_COMMON *cm,