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/rd.h b/av1/encoder/rd.h
index 7651a00..3bbbb64 100644
--- a/av1/encoder/rd.h
+++ b/av1/encoder/rd.h
@@ -453,7 +453,8 @@
 #endif
 }
 
-static INLINE int av1_get_coeff_token_cost(int token, int eob_val, int is_first,
+static INLINE int av1_get_coeff_token_cost(int token, int8_t eob_val,
+                                           int is_first,
                                            const int *head_cost_table,
                                            const int *tail_cost_table) {
   if (eob_val == LAST_EOB) return av1_cost_zero(128);