[riscv-port-jdk11u:riscv-port] RFR: 8287552: riscv: Fix comment typo in li64

[Dingli Zhang]

Please review this backport to riscv-port-jdk11u.
Backport of [JDK-8287552](https://bugs.openjdk.java.net/browse/JDK-8287552). Applies not cleanly because [JDK-8339248](https://bugs.openjdk.org/browse/JDK-8339248) remove li64 macro assembler routine and related code. 
So this patch only unifies the immediate type in movptr_with_offset to int64_t.

Testing:

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

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

Changes: https://git.openjdk.org/riscv-port-jdk11u/pull/29/files
  Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk11u&pr=29&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287552
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/riscv-port-jdk11u/pull/29.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk11u.git pull/29/head:pull/29

PR: https://git.openjdk.org/riscv-port-jdk11u/pull/29