ctrl_get_reference does not need user_priv.

The relationship of the user private data at runtime
is not preserved from decode() to this call which may
occur at an unknown point in the future

Change-Id: Ia7eb25365c805147614574c3af87aedbe0305fc6

test/user_priv_test.cc

diff --git a/test/user_priv_test.cc b/test/user_priv_test.cc
index f9aef33..22fce85 100644
--- a/test/user_priv_test.cc
+++ b/test/user_priv_test.cc
@@ -78,7 +78,7 @@
         ref.idx = rnd.Rand8() % 3;
         decoder.Control(VP9_GET_REFERENCE, &ref);
 
-        CheckUserPrivateData(ref.img.user_priv, &frame_num);
+        CheckUserPrivateData(ref.img.user_priv, NULL);
       }
       md5.Add(img);
     }

vp9/vp9_dx_iface.c

diff --git a/vp9/vp9_dx_iface.c b/vp9/vp9_dx_iface.c
index 3a73eea..746fab0 100644
--- a/vp9/vp9_dx_iface.c
+++ b/vp9/vp9_dx_iface.c
@@ -671,7 +671,7 @@
     VP9Worker *const worker = ctx->frame_workers;
     FrameWorkerData *const worker_data = (FrameWorkerData *)worker->data1;
     vp9_get_reference_dec(worker_data->pbi, data->idx, &fb);
-    yuvconfig2image(&data->img, fb, worker_data->user_priv);
+    yuvconfig2image(&data->img, fb, NULL);
     return VPX_CODEC_OK;
   } else {
     return VPX_CODEC_INVALID_PARAM;