[riscv-port-jdk17u:riscv-port] RFR: 8287552: riscv: Fix comment typo in li64

[Dingli Zhang]

Please review this backport to riscv-port-jdk17u.
Backport of [JDK-8287552](https://bugs.openjdk.java.net/browse/JDK-8287552). Applies cleanly.

Testing:

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

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Commit messages:
 - 8287552: riscv: Fix comment typo in li64

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/7/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=7&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287552
  Stats: 5 lines in 2 files changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/7.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u pull/7/head:pull/7

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/7