Use type with smaller size

This is to reduce the size of the huge token buffer by at least more
than 10%.

BUG=aomedia:940

Change-Id: I2ee7f7f62e8e8fb819cf7fba40a7ca7f860acaa4
diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index 99a9bf3..6760e26 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -1614,7 +1614,7 @@
   int(*tail_token_costs)[COEFF_CONTEXTS][TAIL_TOKENS] =
       x->token_tail_costs[tx_size_ctx][type][ref];
   const int seg_eob = av1_get_tx_eob(&cm->seg, mbmi->segment_id, tx_size);
-  int eob_val;
+  int8_t eob_val;
 
 #if CONFIG_HIGHBITDEPTH
   const int cat6_bits = av1_get_cat6_extrabits_size(tx_size, xd->bd);