eslint-plugin-react-hooks version: 4.2.0

## Steps To Reproduce

I know it shouldn't exist in production code, but it's annoying while editing some files.

```js
import React, { useEffect } from "react";

const App = () => {
  useEffect(); // <-
  return null;
};

export default App;
```

Link to code example: https://codesandbox.io/s/polished-sun-3wr27?file=/src/App.js

## The current behavior

ESLint crashed.

```
TypeError: Cannot read property 'type' of undefined
```

## The expected behavior

ESLint doesn't crash but reports an error instead.
references.forEach(reference => {
          if (reference.writeExpr) {
            reportStaleAssignment(reference.writeExpr, key);
          }
        });
      });
      if (staleAssignments.size > 0) {
        
        return;
      }
      if (!declaredDependenciesNode) {
        
        
        let setStateInsideEffectWithoutDeps = null;
        dependencies.forEach(({isStable, references}, key) => {
          if (setStateInsideEffectWithoutDeps) {
            return;
          }
          references.forEach(reference => {
            if (setStateInsideEffectWithoutDeps) {
              return;
            }
            const id = reference.identifier;
            const isSetState = setStateCallSites.has(id);
            if (!isSetState) {
              return;
            }
            let fnScope = reference.from;
            while (fnScope.type !== 'function') {
              fnScope = fnScope.upper;