hg: shenandoah/jdk9/hotspot: Fix aarch64 compilation error due to shenandoah_wb change

[zgu at redhat.com]

Changeset: 5ea583381dc1
Author:    zgu
Date:      2017-06-20 07:13 -0400
URL:       http://hg.openjdk.java.net/shenandoah/jdk9/hotspot/rev/5ea583381dc1

Fix aarch64 compilation error due to shenandoah_wb change

! src/cpu/aarch64/vm/stubGenerator_aarch64.cpp