RFR: 8349142: [JMH] compiler.MergeLoadBench.getCharBV fails

[SendaoYan]

Hi all,

There are two JMH tests fails after [JDK-8344168](https://bugs.openjdk.org/browse/JDK-8344168) merged. This PR fix the JMH tests fails same as https://github.com/oracle/graal/pull/10602, just cast the second argument of VarHandle.get from long to int.
Change has been verified locally, test-fix only, no risk.

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Commit messages:
 - 8349142: [JMH] compiler.MergeLoadBench.getCharBV fails

Changes: https://git.openjdk.org/jdk/pull/23393/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23393&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349142
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/23393.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23393/head:pull/23393

PR: https://git.openjdk.org/jdk/pull/23393