vp9: Add key_frame condition to is_reference check for loopfilter.

This condiiton is not needed as key_frame should set the refresh
of the reference frames, but good to have for clarity in condition.

Change-Id: Icf9838e7e4f0ff5cf0a9562ae3b5d6c7e6f78702

vp9/encoder/vp9_encoder.c

@@ -2619,8 +2619,8 @@ static void loopfilter_frame(VP9_COMP *cpi, VP9_COMMON *cm) {
   struct loopfilter *lf = &cm->lf;
 
   const int is_reference_frame =
-      (cpi->refresh_last_frame || cpi->refresh_golden_frame ||
-       cpi->refresh_alt_ref_frame);
+      (cm->frame_type == KEY_FRAME || cpi->refresh_last_frame ||
+       cpi->refresh_golden_frame || cpi->refresh_alt_ref_frame);
 
   if (xd->lossless) {
     lf->filter_level = 0;