RFR: 8361536: [s390x] Saving return_pc at wrong offset

[Amit Kumar]

Fixes the bug where return pc was stored at a wrong offset, which causes issue with java abi. 

Issue appeared in #26004, see the comment: https://github.com/openjdk/jdk/pull/26004#issuecomment-3017928879.

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Commit messages:
 - Revert "save another 8 bytes"
 - save another 8 bytes
 - fix

Changes: https://git.openjdk.org/jdk/pull/26209/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26209&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8361536
  Stats: 20 lines in 1 file changed: 2 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/26209.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26209/head:pull/26209

PR: https://git.openjdk.org/jdk/pull/26209