lavc/dovi_rpu: Fix UB for possible left shift of negative values

It is undefined to left-shift a negative value.

libavcodec/dovi_rpu.c

@@ -172,7 +172,7 @@ static inline int64_t get_se_coef(GetBitContext *gb, const AVDOVIRpuDataHeader *
     case RPU_COEFF_FIXED:
         ipart = get_se_golomb_long(gb);
         fpart.u32 = get_bits_long(gb, hdr->coef_log2_denom);
-        return (ipart << hdr->coef_log2_denom) + fpart.u32;
+        return ipart * (1LL << hdr->coef_log2_denom) + fpart.u32;
 
     case RPU_COEFF_FLOAT:
         fpart.u32 = get_bits_long(gb, 32);