[riscv-port-jdk11u:riscv-port] RFR: 8294012: RISC-V: get/put_native_u8 missing the case when address&7 is 6

[Dingli Zhang]

Hi all, 

Please review this backport to riscv-port-jdk11u.

Backport of [JDK-8294012](https://bugs.openjdk.org/browse/JDK-8294012). Applies cleanly.

Testing:
- Tier1 passed without new failure on lp4a (release).

-------------

Commit messages:
 - 8294012: RISC-V: get/put_native_u8 missing the case when address&7 is 6

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/37/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=37&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294012
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/37.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/37/head:pull/37

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/37