Caught and fixed a typo in r262572.

I should have checked and imported D's in-class initializer.
Instead I accidentally used ToField's in-class initializer,
which is always NULL so ToField will never get one.

<rdar://problem/24943405>


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@262576 91177308-0d34-0410-b5e6-96231b3b80d8