RFR(T): 8216482: Shenandoah: typo in ShenandoahBarrierSetC2::clone_barrier_at_expansion() causes failed compilations

[Roland Westrelin]

FTR, I pushed this one by mistake to jdk/jdk instead of jdk12. I read
in:

https://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2019-January/024470.html

that it's ok to push a change to 12 after jdk/jdk so I will do that.

Roland.