Rename a couple of variables to be more accurate.

It's not really a "ScopeDIE", as such - it's the abstract function
definition's DIE. And we usually use "SP" for subprograms, rather than
"Sub".

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209499 91177308-0d34-0410-b5e6-96231b3b80d8