[Format] Fix incorrect pointer/reference detection

https://llvm.org/PR50568

When an overloaded operator is called, its argument must be an
expression.

Before:
    void f() { a.operator()(a *a); }

After:
    void f() { a.operator()(a * a); }

Reviewed By: HazardyKnusperkeks, curdeius, MyDeveloperDay

Differential Revision: https://reviews.llvm.org/D103678