RFR: 8322278: Generational ZGC: Adjust ZHeuristics::use_per_cpu_shared_small_pages to meet its comment

[Guoxiong Li]

Hi all,

This trivial patch fixes the method `ZHeuristics::use_per_cpu_shared_small_pages` to meet its comment.

Thanks for the review.

Best Regards,
-- Guoxiong

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Commit messages:
 - Adjust ZHeuristics::use_per_cpu_shared_small_pages to meet its comment

Changes: https://git.openjdk.org/jdk/pull/17138/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17138&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322278
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17138.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17138/head:pull/17138

PR: https://git.openjdk.org/jdk/pull/17138