Cannot insert docstrings for C functions with struct arguments

If a C function is declared like:

```
struct point {
    int x;
    int y;
};

int foo(struct point p) {
     return p.x + p.y;
}
```

`ts-docstr-at-point` will fail with the error:

`user-error: Multiple declarations are invalid, 2`.

I think this is triggered by the use of the `struct` keyword, as a basic or typedef name won't cause this issue.