RFR: 8254166: Zero: return-type warning in zeroInterpreter_zero.cpp

[Aleksey Shipilev]

This breaks 11u without disabled warnings as errors, but the issue exists in head JDK as well. Might as well fix it
everywhere.

Testing:
  - [x] Linux ARM32 Zero build on HEAD JDK
  - [x] Linux ARM32 Zero build on 11u

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

Commit messages:
 - 8254166: Zero: return-type warning in zeroInterpreter_zero.cpp

Changes: https://git.openjdk.java.net/jdk/pull/545/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=545&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254166
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/545.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/545/head:pull/545

PR: https://git.openjdk.java.net/jdk/pull/545