Fix a out-of-bounds accessing bug.

Before applying this modification, when executing the benchmark listed below, a segment fault will be reported because of the out-of-bounds accessing to the packed_weights buffer:

./x16-packw-bench --benchmark_filter=qs8_qc4w_packw_x8c8__reference/sd1x_diffusion/B:8/M:4096/N:4096/K:40/real_time --benchmark_min_time=0.1

Now, the packed_weights buffer is resized and the bug is fixed.

bench/packw-benchmark.h

@@ -272,7 +272,7 @@ static void qs8_qc4w_packw(benchmark::State& state,
 
   const size_t rounded_n = benchmark::utils::RoundUp(dim_n, nr);
   const size_t rounded_k = benchmark::utils::RoundUp(dim_k, kr * sr);
-  const size_t rounded_size = rounded_n * rounded_k / 2 + rounded_n * sizeof(uint32_t);
+  const size_t rounded_size = rounded_n * rounded_k + rounded_n * sizeof(uint32_t);
 
   std::random_device random_device;
   auto rng = std::mt19937(random_device());