RFR: 8334715: [riscv] Mixed use of tab and whitespace in riscv.ad

[SendaoYan]

Hi all,
  Trivial fix the mixed use of tab and whitespace in `src/hotspot/cpu/riscv/riscv.ad`, no risk.

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Commit messages:
 - 8334715: [riscv] Mix use of tab and whitespace in riscv.ad

Changes: https://git.openjdk.org/jdk/pull/19823/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19823&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334715
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/19823.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19823/head:pull/19823

PR: https://git.openjdk.org/jdk/pull/19823