Change cm back to const in combined_motion_search

The local variable cm in combined_motion_search() was changed to a
non-const pointer so that it could be passed to get_ref_scale_factors().
There is a get_ref_scale_factors_const() function for this purpose.

A follow-up to commit a047955.

Bug: 495477995, 495996858
Change-Id: Ic8b66f8060247a3487a7740fe5383c6e5455fa10

av1/encoder/nonrd_pickmode.c

diff --git a/av1/encoder/nonrd_pickmode.c b/av1/encoder/nonrd_pickmode.c
index 3835599..024dae6 100644
--- a/av1/encoder/nonrd_pickmode.c
+++ b/av1/encoder/nonrd_pickmode.c
@@ -192,7 +192,7 @@
                                   int *rate_mv, int64_t best_rd_sofar,
                                   int use_base_mv) {
   MACROBLOCKD *xd = &x->e_mbd;
-  AV1_COMMON *cm = &cpi->common;
+  const AV1_COMMON *cm = &cpi->common;
   const SPEED_FEATURES *sf = &cpi->sf;
   MB_MODE_INFO *mi = xd->mi[0];
   int step_param = (sf->rt_sf.fullpel_search_step_param)
@@ -207,7 +207,7 @@
   int cost_list[5];
   int search_subpel = 1;
 
-  if (av1_is_scaled(get_ref_scale_factors(cm, ref))) {
+  if (av1_is_scaled(get_ref_scale_factors_const(cm, ref))) {
     const YV12_BUFFER_CONFIG *scaled_ref = av1_get_scaled_ref_frame(cpi, ref);
     (void)scaled_ref;
     assert(scaled_ref != NULL);