Fix int overflow in decode_coefs()

BUG=b/69205191

Change-Id: I79e404dc2cd6db06e71a64338b74eb4b575ba431

av1/decoder/detokenize.c

diff --git a/av1/decoder/detokenize.c b/av1/decoder/detokenize.c
index 728115a..b1a9705 100644
--- a/av1/decoder/detokenize.c
+++ b/av1/decoder/detokenize.c
@@ -199,7 +199,7 @@
       dqv = ((iqmatrix[scan[c]] * (int)dqv) + (1 << (AOM_QM_BITS - 1))) >>
             AOM_QM_BITS;
 #endif
-    v = (val * dqv) >> dq_shift;
+    v = (int)(((int64_t)val * dqv) >> dq_shift);
 #endif
 
     v = (int)check_range(aom_read_bit(r, ACCT_STR) ? -v : v, xd->bd);