RFR: 8144315: update_rs is passed wrong object

[Erik Helin]

Hi all,

this patch fixes an issue with the patch for JDK-8144067. The problem is
that the wrong oop is passed to update_rs when 'obj' gets forwarded.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8144315

Webrev:
http://cr.openjdk.java.net/~ehelin/8144315/webrev.00/

Testing:
- GC Basher with full verification
- GC test suite with full verification
- JPRT

Thanks,
Erik