Change left shift to multiply

Negative distortion is used in trellis quant process for RDcost
computation, this change avoids compiler warning on "left shift
of negative values".

Change-Id: Iaea0ffebb6c9236e779e36301fbc69b180be1f3d

av1/encoder/rd.h

@@ -29,7 +29,7 @@ extern "C" {
 
 #define RDCOST(RM, R, D)                                          \
   (ROUND_POWER_OF_TWO(((int64_t)R) * (RM), AV1_PROB_COST_SHIFT) + \
-   (D << RDDIV_BITS))
+   (D * (1 << RDDIV_BITS)))
 
 #define RDCOST_DBL(RM, R, D)                                       \
   (((((double)(R)) * (RM)) / (double)(1 << AV1_PROB_COST_SHIFT)) + \