[riscv-port-jdk17u:riscv-port] RFR: 8296136: Use correct register in aarch64_enc_fast_unlock()

[Gui Cao]

Please help review this backport to riscv-port-jdk17u.
Backport of [JDK-8296136](https://bugs.openjdk.org/browse/JDK-8296136).

Testing:

- Tier1 passed without new failure on qemu (release).

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Commit messages:
 - backport 8296136: Use correct register in aarch64_enc_fast_unlock()

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/27/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=27&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296136
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/27.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u.git pull/27/head:pull/27

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/27