[llvm] [AArch64] Change IssueWidth to 6 in AArch64SchedNeoverseV2.td (PR #142565)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm approved this pull request.

If @sjoerdmeijer's data reflects our own measurements then this PR looks go to me.

https://github.com/llvm/llvm-project/pull/142565