For the following example:
```
fun foo(bar: Int) {
<expr>if (bar == 4) return "Four"
else return "Int"</expr>
}
```
AA FE1.0 `isUsedAsExpression` returns `false`.
Since the current AA FIR `isUsedAsExpression` returns `true` for the
above example, this commit fixes it.
Jaebaek Seo