Enforce motion search range clamp for sub8x8

This commit constrains the maximal motion search range for sub8x8
blocks to be [-1023, 1023], in the unit of full pixel.

Change-Id: I955b60649364ab410f2453cafd46a496f2fcb43e

vp9/encoder/vp9_rdopt.c

diff --git a/vp9/encoder/vp9_rdopt.c b/vp9/encoder/vp9_rdopt.c
index 399c534..fb31f42 100644
--- a/vp9/encoder/vp9_rdopt.c
+++ b/vp9/encoder/vp9_rdopt.c
@@ -1781,6 +1781,9 @@
           further_steps = (MAX_MVSEARCH_STEPS - 1) - step_param;
           // adjust src pointer for this block
           mi_buf_shift(x, i);
+
+          vp9_clamp_mv_min_max(x, &bsi->ref_mv->as_mv);
+
           if (cpi->sf.search_method == HEX) {
             bestsme = vp9_hex_search(x, &mvp_full.as_mv,
                                      step_param,