RFR: 8277985: G1: Compare max_parallel_refinement_threads to UINT_MAX

[Leo Korinth]

The max_parallel_refinement_threads comparison will never be larger than UINTPTR_MAX / divisor on platforms where pointers are larger than unsigned,   Use the intended UINT_MAX instead.

-------------

Commit messages:
 - 8277985: G1: Compare max_parallel_refinement_threads to UINT_MAX

Changes: https://git.openjdk.java.net/jdk/pull/6617/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6617&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277985
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6617.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6617/head:pull/6617

PR: https://git.openjdk.java.net/jdk/pull/6617