Fix overloaded static functions in SemaCodeComplete

https://bugs.llvm.org/show_bug.cgi?id=33904
Happens when static function is accessed via the class variable. That leads to incorrect overloads number because the variable is considered as the first argument.

struct Bar {
  static void foo(); static void foo(int);
};

int main() {
  Bar b;
  b.foo(/*complete here*/); // did not work before
  Bar::foo(/*complete here*/); // worked fine
}

Patch by Ivan Donchevskii!

Differential Revision: https://reviews.llvm.org/D36390

llvm-svn: 316646