RFR: 8320399: RISC-V: Some format clean-up in opto assembly code

[Feilong Jiang]

Hi, please review this trivial clean-up in riscv.ad and c2_macroAssembler_riscv.cpp:
- Some C2 instructions are missing the `done` label at the end of the format string. 
- Fix format naming error in `MoveF2I_reg_reg` and `MoveL2D_reg_reg`.
- Small code adjustments to `C2_MacroAssembler::string_compare`.

Testing:
- [x] GHA linux-riscv cross-compiling

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

Commit messages:
 - clean up riscv opto format

Changes: https://git.openjdk.org/jdk/pull/16734/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16734&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320399
  Stats: 23 lines in 2 files changed: 6 ins; 0 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/16734.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16734/head:pull/16734

PR: https://git.openjdk.org/jdk/pull/16734