Cleanup: Use the appropriate API for accessing the DIVariable of a
DBG_VALUE intrinsic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217533 91177308-0d34-0410-b5e6-96231b3b80d8
Remember to eraseFromParent after replaceAllUsesWith.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217536 91177308-0d34-0410-b5e6-96231b3b80d8