Re-use switchable rate value in handle_inter_mode

The value of switchable rate has been stored in a local variable.
This change skips the second call to vp9_get_switchable_rate() by
reusing the local variable.

Change-Id: Ib7d3fef7621cc4bde94c6d6e6b3a71f1fd4559f2
diff --git a/vp9/encoder/vp9_rdopt.c b/vp9/encoder/vp9_rdopt.c
index 053dbbb..3a34e6f 100644
--- a/vp9/encoder/vp9_rdopt.c
+++ b/vp9/encoder/vp9_rdopt.c
@@ -2366,7 +2366,7 @@
   }
 
   if (cm->interp_filter == SWITCHABLE)
-    *rate2 += vp9_get_switchable_rate(cpi);
+    *rate2 += rs;
 
   if (!is_comp_pred) {
     if (cpi->allow_encode_breakout)