Add an identity scale factor in AV1_COMMON

Set up the identity scale factor once per frame, instead of per joint
motion search.

Change-Id: I5edd264655254f4b6a0a923d8ab43adbca044228
diff --git a/av1/encoder/encoder.c b/av1/encoder/encoder.c
index cffdffe..9d56407 100644
--- a/av1/encoder/encoder.c
+++ b/av1/encoder/encoder.c
@@ -4967,11 +4967,9 @@
     }
   }
 
-#if CONFIG_INTRABC
-  av1_setup_scale_factors_for_frame(&xd->sf_identity, cm->width, cm->height,
+  av1_setup_scale_factors_for_frame(&cm->sf_identity, cm->width, cm->height,
                                     cm->width, cm->height,
                                     cm->use_highbitdepth);
-#endif  // CONFIG_INTRABC
 
   set_ref_ptrs(cm, xd, LAST_FRAME, LAST_FRAME);
 }