Port simplified rdmult computation from libvpx

Change-Id: Id4d4e1c87d8df8657d7b3c488a777d67906f4491
diff --git a/av1/encoder/rd.h b/av1/encoder/rd.h
index 6250df6..2e2a30d 100644
--- a/av1/encoder/rd.h
+++ b/av1/encoder/rd.h
@@ -643,8 +643,7 @@
 struct AV1_COMP;
 struct macroblock;
 
-int64_t av1_compute_rd_mult_based_on_qindex(const struct AV1_COMP *cpi,
-                                            int qindex);
+int av1_compute_rd_mult_based_on_qindex(const struct AV1_COMP *cpi, int qindex);
 
 int av1_compute_rd_mult(const struct AV1_COMP *cpi, int qindex);