RFR: JDK-8251926: [PPC] Removed an unused variable in assembler_ppc.cpp

[Sorna Sarathi]

This PR removes an unused variable from load_const_optimized function in assembler_ppc.cpp file.

JBS Issue: [JDK-8251926](https://bugs.openjdk.org/browse/JDK-8251926)

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Commit messages:
 - Removed an unused variable in assembler_ppc.cpp file

Changes: https://git.openjdk.org/jdk/pull/21874/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21874&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8251926
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21874.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21874/head:pull/21874

PR: https://git.openjdk.org/jdk/pull/21874