Use the left neighbor in under 4x4 chroma obmc

Will introduce 0.03% improvement compared to using
the above neighbor.

Change-Id: I1e45db1152cd74680f010d19bffd37276e826bce

av1/common/reconinter.c

diff --git a/av1/common/reconinter.c b/av1/common/reconinter.c
index 7d2d9ae..112b1c4 100644
--- a/av1/common/reconinter.c
+++ b/av1/common/reconinter.c
@@ -1749,7 +1749,7 @@
 #else
     case BLOCK_4X4:
     case BLOCK_8X4:
-    case BLOCK_4X8: return dir == 1; break;
+    case BLOCK_4X8: return dir == 0; break;
 #endif
     default: return 0;
   }