Correct bug in loopfilter initialization

The memset sets 16 bytes rather than the correct size of the
final array dimension (MAX_MODE_LF_DELTAS).

(In response to bug posted by Manjit Hota to codec-devel
and webm-discuss lists)

Change-Id: I8980f5aa71ddc9d7ef57c5b4700bc28ddf8651c7

vp9/common/vp9_loopfilter.c

@@ -108,7 +108,7 @@ void vp9_loop_filter_frame_init(VP9_COMMON *const cm, MACROBLOCKD *const xd,
     if (!lf->mode_ref_delta_enabled) {
       // we could get rid of this if we assume that deltas are set to
       // zero when not in use; encoder always uses deltas
-      vpx_memset(lfi->lvl[seg_id][0], lvl_seg, 4 * 4);
+      vpx_memset(lfi->lvl[seg_id][0], lvl_seg, sizeof(lfi->lvl[seg_id][0]));
       continue;
     }