RFR: 8255859: Incorrect comments in log.hpp

[Ioi Lam]

Please review this trivial, comment-only change. I updated the comments to match the current usage for `Log` and `LogTarget`. I also tried to make the examples consistent so you can easily see the difference between `Log` and `LogTarget`.

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Commit messages:
 - 8255859: Incorrect comments in log.hpp

Changes: https://git.openjdk.java.net/jdk/pull/2785/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2785&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255859
  Stats: 14 lines in 1 file changed: 1 ins; 3 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2785.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2785/head:pull/2785

PR: https://git.openjdk.java.net/jdk/pull/2785