Fix division rounding in OPTFLOW_REFINEMENT

This slightly improves the precision of refined MV.

Change-Id: I46430346bbdc67d25270c554fc11bf38b8c8744a

av1/common/reconinter.h

diff --git a/av1/common/reconinter.h b/av1/common/reconinter.h
index 5e459e8..a6afd5f 100644
--- a/av1/common/reconinter.h
+++ b/av1/common/reconinter.h
@@ -295,8 +295,8 @@
   if (use_optflow_refinement) {
     // optflow refinement always returns MVs with 1/16 precision so it is not
     // necessary to shift the MV before clamping
-    clamped_mv.row = (int16_t)(src_mv->row >> ss_y);
-    clamped_mv.col = (int16_t)(src_mv->col >> ss_x);
+    clamped_mv.row = (int16_t)ROUND_POWER_OF_TWO_SIGNED(src_mv->row, ss_y);
+    clamped_mv.col = (int16_t)ROUND_POWER_OF_TWO_SIGNED(src_mv->col, ss_x);
 
   } else {
     clamped_mv.row = (int16_t)(src_mv->row * (1 << (1 - ss_y)));