RFR: 8253938: ZGC: Clean up argument names after JDK-8253030

[Albert Mingkun Yang]

On Fri, 2 Oct 2020 15:30:22 GMT, Per Liden <pliden at openjdk.org> wrote:

> JDK-8253030 changed some variable names from timeout_in_millis to timeout_in_micros, but missed to do the same rename
> in the header file. This trivial patch renames two arguments in zMark.hpp accordingly.

Marked as reviewed by ayang (Author).

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PR: https://git.openjdk.java.net/jdk/pull/483