Don't patch the storage class of static data members.

This removes a bit of patching that survived r178663. Without it we can produce
better a better error message for

const int a = 5;
static const int a;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178795 91177308-0d34-0410-b5e6-96231b3b80d8