RFR(XXS) 8187331: VirtualSpaceList tracks free space on wrong node

[Zhengyu Gu]

Please review one line fix on reporting metaspace virtual space's free 
space (See bug for details)

This bug causes metaspace statistics data not adding up.


Bug: https://bugs.openjdk.java.net/browse/JDK-8187331
Webrev: http://cr.openjdk.java.net/~zgu/8187331/webrev.00/


Test:

hotspot_tier1_runtime on Linux 64 (fastdebug and release)

Thanks,

-Zhengyu