LPF_SB: select filter level and apply for superblock

For each superblock, select the best deblocking filter level and apply
filtering. The filter level is signaled to decoder using a delta based
scheme.

Change-Id: I53e32589cabac9e2a4e580808fdd39ac878fe8c6
diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 12d69ee..3b83d0c 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -2295,7 +2295,7 @@
   // send filter level for each superblock (64x64)
   if (bsize == cm->sb_size) {
     if (mi_row == 0 && mi_col == 0) {
-      aom_write_literal(w, cm->mi_grid_visible[0]->mbmi.filt_lvl, 6);
+      aom_write_literal(w, cm->mi[0].mbmi.filt_lvl, 6);
       cm->mi_grid_visible[0]->mbmi.reuse_sb_lvl = 0;
       cm->mi_grid_visible[0]->mbmi.delta = 0;
       cm->mi_grid_visible[0]->mbmi.sign = 0;