RFR: 8337788: RISC-V: Cleanup code in MacroAssembler::reserved_stack_check

[Gui Cao]

Hi, 
In the MacroAssembler::reserved_stack_check() function:

    RuntimeAddress target(StubRoutines::throw_delayed_StackOverflowError_entry());
    relocate(target.rspec(), [&] {
      int32_t offset;
      movptr(t0, target.target(), offset);
      jr(t0, offset);
    });

can be simplified to:

  la(t0, RuntimeAddress(StubRoutines::throw_delayed_StackOverflowError_entry()));
  jr(t0);


In addition, the code formatting has been modified to remove the extra spaces before the code.

Please take a look and have some reviews. Thanks a lot.

### Testing
- [x] Run tier1-3 tests on SOPHON SG2042 (fastdebug)

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

Commit messages:
 - JDK-8337788: RISC-V: Cleanup code in MacroAssembler::reserved_stack_check

Changes: https://git.openjdk.org/jdk/pull/20458/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20458&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337788
  Stats: 19 lines in 1 file changed: 0 ins; 4 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/20458.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20458/head:pull/20458

PR: https://git.openjdk.org/jdk/pull/20458