filter-intra: fix compiler warnings when cb4x4 is off

Change-Id: I995b1ba6b1dafeceb1e75a3d71d6630215a8df68
diff --git a/av1/decoder/decodemv.c b/av1/decoder/decodemv.c
index 988c5ee..1cdbecb 100644
--- a/av1/decoder/decodemv.c
+++ b/av1/decoder/decodemv.c
@@ -782,7 +782,10 @@
                            xd->plane[1].subsampling_x,
                            xd->plane[1].subsampling_y))
     return;
-#endif
+#else
+  (void)mi_row;
+  (void)mi_col;
+#endif  // CONFIG_CB4X4
 
   if (mbmi->uv_mode == DC_PRED
 #if CONFIG_PALETTE