VP9-SVC: Bugfix to allow skipping lower layer(s) encoding.

The setting of svc->spatial_layer_to_encode was missing
in VP9E_SET_SVC_LAYER_ID.

Change-Id: I015b1a64adb9ef2644d6477a02d9d9364c8462b9

vp9/vp9_cx_iface.c

@@ -1373,6 +1373,7 @@ static vpx_codec_err_t ctrl_set_svc_layer_id(vpx_codec_alg_priv_t *ctx,
   SVC *const svc = &cpi->svc;
 
   svc->first_spatial_layer_to_encode = data->spatial_layer_id;
+  svc->spatial_layer_to_encode = data->spatial_layer_id;
   svc->temporal_layer_id = data->temporal_layer_id;
   // Checks on valid layer_id input.
   if (svc->temporal_layer_id < 0 ||