[jstest] Fix Array.p.sort 'sort-lengths' benchmark

This CL fixes wrong parentheses that caused the sort-length benchmark
to generate "random" arrays that only contained zeroes.

R=ishell@chromium.org

Change-Id: Ie2a564da037425a4ef9c2417597cdc13b497e32b
Reviewed-on: https://chromium-review.googlesource.com/1186332Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#55336}

test/js-perf-test/ArraySort/sort-lengths.js

@@ -10,7 +10,7 @@ function SortAsc() {
 
 function Random(length) {
   for (let i = 0; i < length; ++i) {
-    array_to_sort.push(Math.floor(Math.random()) * length);
+    array_to_sort.push(Math.floor(Math.random() * length));
   }
   AssertPackedSmiElements();
 }