[test] Speed up regress-crbug-319860.js

This reduces the time it takes to run this test in --jitless mode
from 32s to 0.7s.

Bug: v8:9416
Change-Id: Ie9a7465b604b28ff8ccaa50f0918c62e3128ac08
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1682575
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62464}

test/mjsunit/regress/regress-crbug-319860.js

@@ -43,6 +43,6 @@ read(a, 0);
 %OptimizeFunctionOnNextCall(read);
 
 // Segfault maybe?
-for (var i = 0; i > -1000000; --i) {
-  read(a, i);
+for (var i = 0; i > -100000; i -= 987) {
+  assertEquals(0, read(a, i));
 }