RFR: 8264885: Fix the code style of macro in aarch64_neon_ad.m4

[Wang Huang]

* trivial fix
* align the comment of macros

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Commit messages:
 - 8264885: Fix the code style of macro in aarch64_neon_ad.m4

Changes: https://git.openjdk.java.net/jdk/pull/3395/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3395&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264885
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3395.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3395/head:pull/3395

PR: https://git.openjdk.java.net/jdk/pull/3395