RFR: 8156028: G1YoungGenSizer _adaptive_size not correct when setting NewSize and MaxNewSize to the same value

[Stefan Johansson]

Please review this small change for:
https://bugs.openjdk.java.net/browse/JDK-8156028

Webrev:
http://cr.openjdk.java.net/~sjohanss/8156028/hotspot.00/

Summary:
The comparison in G1YoungGenSizer is wrong, when NewSize and MaxNewSize 
is equal the sizer should not be adaptive.

Testing:
* JPRT
* RBT

Thanks,
Stefan