It turns out the problem was a bit more wide-spread. Removing a lot of unneeded typecasts. getScopeRep() already returns a NestedNameSpecifier.

No functional changes intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198414 91177308-0d34-0410-b5e6-96231b3b80d8