Don't set the bmi mode when doing error concealment

Since the block will be interpreted as an inter block, the mode will
be interpreted as a motion vector, resulting in bad concealment.

Change-Id: Ifcc685ae1cc883492bce6dbd61e418d91a89b053
diff --git a/vp8/decoder/error_concealment.c b/vp8/decoder/error_concealment.c
index 4f8f1a6..7051bb9 100644
--- a/vp8/decoder/error_concealment.c
+++ b/vp8/decoder/error_concealment.c
@@ -567,7 +567,6 @@
             else
             {
                 mv->as_int = 0;
-                mi->bmi[row*4 + col].as_mode = NEW4X4;
                 mi->mbmi.need_to_clamp_mvs = 0;
             }
         }