Fix a compile warning with dual-filter off

Change-Id: I68bb6ea8e26efe44bbbfb0f1a956620578578d55

av1/common/reconinter.h

diff --git a/av1/common/reconinter.h b/av1/common/reconinter.h
index 9465821..7ea4289 100644
--- a/av1/common/reconinter.h
+++ b/av1/common/reconinter.h
@@ -110,10 +110,10 @@
                                           const InterpFilter interp_filter,
 #endif
                                           int xs, int ys, int bd) {
-  const int ref = conv_params->ref;
   const int avg = conv_params->do_average;
   assert(avg == 0 || avg == 1);
 #if CONFIG_DUAL_FILTER
+  const int ref = conv_params->ref;
   const InterpFilterParams interp_filter_params_x =
       av1_get_interp_filter_params(interp_filter[1 + 2 * ref]);
   const InterpFilterParams interp_filter_params_y =