RFR: 8322195: RISC-V: Minor improvement of MD5 instrinsic

[Hamlin Li]

Hi,
Can you review this minor patch to improve MD5 instrinsic?
Thanks!

## Test

tests (`find test/ -iname "*md5*.java"`) passed.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/17123/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17123&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322195
  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17123.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17123/head:pull/17123

PR: https://git.openjdk.org/jdk/pull/17123