RFR: 8237884: ZGC: Use clamp() instead of MIN2(MAX2())

[Kim Barrett]

> On Jan 27, 2020, at 8:54 AM, Per Liden <per.liden at oracle.com> wrote:
> 
> JDK-8233702 introduced clamp(), but ZHeuristics still uses MIN2(MAX2()) in one place.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8237884
> Webrev: http://cr.openjdk.java.net/~pliden/8237884/webrev.0
> 
> /Per

Looks good.