RFR: 8315743: RISC-V: Cleanup masm lr()/sc() methods

[Robbin Ehn]

Hi, please consider this small cleanup.

Tested tier1

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Commit messages:
 - Use lr()/sc()

Changes: https://git.openjdk.org/jdk/pull/15578/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15578&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315743
  Stats: 17 lines in 2 files changed: 2 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/15578.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15578/head:pull/15578

PR: https://git.openjdk.org/jdk/pull/15578