hg: shenandoah/jdk8u/hotspot: Fix build failure: signedness mismatch in assert

[ashipile at redhat.com]

Changeset: febbefbe2de7
Author:    shade
Date:      2018-05-22 11:55 +0200
URL:       http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/febbefbe2de7

Fix build failure: signedness mismatch in assert
Contributed-by: Michal Vala <mvala at redhat.com>

! src/share/vm/gc_implementation/shenandoah/shenandoahHeapRegion.cpp