AArch64: Tidy up a few comments.

Have the comments match the actual parameter names. Found via clang-tidy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215401 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing closing namespace comment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215402 91177308-0d34-0410-b5e6-96231b3b80d8