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

vp8/decoder/error_concealment.c

@@ -567,7 +567,6 @@ static void interpolate_mvs(MACROBLOCKD *mb,
             else
             {
                 mv->as_int = 0;
-                mi->bmi[row*4 + col].as_mode = NEW4X4;
                 mi->mbmi.need_to_clamp_mvs = 0;
             }
         }