Fix enc multi-threading mismatch in screen content

AV1 encoder multi-threading mismatch for --tune-content=screen
has been fixed.

BUG= aomedia:2118

Change-Id: I971b382f6b58b98e67fff78dbdcc1e6d6879aa2b
diff --git a/av1/encoder/encoder.h b/av1/encoder/encoder.h
index 3d0bcab..3ba1354 100644
--- a/av1/encoder/encoder.h
+++ b/av1/encoder/encoder.h
@@ -468,6 +468,7 @@
   FRAME_COUNTS *counts;
   PC_TREE *pc_tree;
   PC_TREE *pc_root[MAX_MIB_SIZE_LOG2 - MIN_MIB_SIZE_LOG2 + 1];
+  uint32_t *hash_value_buffer[2][2];
   int32_t *wsrc_buf;
   int32_t *mask_buf;
   uint8_t *above_pred_buf;