hg: zgc/zgc: ZGC: Fix reserve high/low accounting

[per.liden at oracle.com]

Changeset: ef83b31eed91
Author:    pliden
Date:      2018-06-05 12:06 +0200
URL:       http://hg.openjdk.java.net/zgc/zgc/rev/ef83b31eed91

ZGC: Fix reserve high/low accounting

! src/hotspot/share/gc/z/zStat.cpp