rtc: Fix to usage of svc refresh buffer

For the case where user sets the refresh flags
via the external svc control: when using the array
svc->refresh[], use the correct array index for the
reference frame (i.e., ref_frame_map_idx).

Change-Id: I166bd992b906a9a476f09f26abd3f5d7743938c1
diff --git a/av1/encoder/encode_strategy.c b/av1/encoder/encode_strategy.c
index 51a5cb2..b6def7a 100644
--- a/av1/encoder/encode_strategy.c
+++ b/av1/encoder/encode_strategy.c
@@ -820,7 +820,8 @@
     if (cpi->svc.external_ref_frame_config) {
       for (unsigned int i = 0; i < INTER_REFS_PER_FRAME; i++) {
         int ref_frame_map_idx = cpi->svc.ref_idx[i];
-        refresh_mask |= cpi->svc.refresh[i] << ref_frame_map_idx;
+        refresh_mask |= cpi->svc.refresh[ref_frame_map_idx]
+                        << ref_frame_map_idx;
       }
       return refresh_mask;
     }