One fix in aom_cx_set_ref example

Fixed 1 place in aom_cx_set_ref example to get the correct reference.

Change-Id: I8944cecce389d5f83252edb54b6f762e2d3143fd
diff --git a/examples/aom_cx_set_ref.c b/examples/aom_cx_set_ref.c
index e02e94c..fc037d4 100644
--- a/examples/aom_cx_set_ref.c
+++ b/examples/aom_cx_set_ref.c
@@ -163,7 +163,7 @@
 
         // Copy out first decoded frame, and use it as reference later.
         if (*frame_out == 1 && ext_ref != NULL)
-          if (aom_codec_control(dcodec, AV1_GET_NEW_FRAME_IMAGE, ext_ref))
+          if (aom_codec_control(dcodec, AV1_COPY_NEW_FRAME_IMAGE, ext_ref))
             die_codec(dcodec, "Failed to get decoder new frame");
       }
     }