RFR: 8294012: [riscv] get/put_native_u8 missing the case when address&7 is 6

[Vladimir Kempik]

Please review this small fix, making get/put_native_u8 a slightly more efficient on riscv
original code misses the case when address AND 7 is 6, and making such cases to be read/write with a 1 byte move.

Test results on risc-v to follow soon.

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Commit messages:
 - [riscv] get/put_native_u8 missing the case when address&7 is 6

Changes: https://git.openjdk.org/jdk/pull/10344/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10344&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/jdk/pull/10344.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10344/head:pull/10344

PR: https://git.openjdk.org/jdk/pull/10344