RFR: 8347923: Parallel: Simplify compute_survivor_space_size_and_threshold

[Albert Mingkun Yang]

Trivial extracting out the common subexpression from both if-else branches.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/23155/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23155&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347923
  Stats: 5 lines in 1 file changed: 0 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/23155.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23155/head:pull/23155

PR: https://git.openjdk.org/jdk/pull/23155