RFR: 8318805: RISC-V: Wrong comments instructions cost in riscv.ad

[Hamlin Li]

Hi,
Can you review this minor change in the comments of riscv.ad for the instruction cost?
Thanks!

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16357/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16357&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318805
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16357.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16357/head:pull/16357

PR: https://git.openjdk.org/jdk/pull/16357