RFR: 8305944: assert(is_aligned(ref, HeapWordSize)) failed: invariant

[SUN Guoyun]

For narrowOop, the alignment should be sizeof(narrowOop) instead of HeapWordSize.

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Commit messages:
 - 8305944: assert(is_aligned(ref, HeapWordSize)) failed: invariant

Changes: https://git.openjdk.org/jdk/pull/13471/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13471&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305944
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13471.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13471/head:pull/13471

PR: https://git.openjdk.org/jdk/pull/13471