RFR: 8305112: RISC-V: Typo fix for RVC description

[Xiaolin Zheng]

Fix trivial typos in the RVC description that may cause confusion. Found in backporting process https://github.com/openjdk/riscv-port-jdk17u/pull/28.

Thanks,
Xiaolin

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Commit messages:
 - Typo fix

Changes: https://git.openjdk.org/jdk/pull/13219/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13219&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305112
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13219.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13219/head:pull/13219

PR: https://git.openjdk.org/jdk/pull/13219