RFR: 8365841: RISC-V: Several IR verification tests fail after JDK-8350960 without Zvfh

[Dingli Zhang]

Hi,
Can you help to review this patch? Thanks!

The error in both cases is caused by the same reason: the target IR, MulReductionVI, is not matched.
This is because the match_rule_supported_vector in riscv_v.ad is missing a break. If the if condition in `case MulReductionVI` evaluates to false, the loop will not exit until the `return UseZvfh`.

Failed IR tests:
compiler/loopopts/superword/ProdRed_Int.java
compiler/loopopts/superword/RedTest_int.java

### Test (fastdebug)
- [x] Run compiler/loopopts/superword/ProdRed_Int.java on k1 and k230
- [x] Run compiler/loopopts/superword/RedTest_int.java on k1 and k230

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

Commit messages:
 - 8365841: RISC-V: Several IR verification tests fail after JDK-8350960 without Zvfh

Changes: https://git.openjdk.org/jdk/pull/26854/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26854&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365841
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26854.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26854/head:pull/26854

PR: https://git.openjdk.org/jdk/pull/26854