Fix ArrowFunctionExpression with body being an expression

[Andarist]

const example = () => (theme = <ThemeContext.Consumer />)

this is likely broken because of https://github.com/Andarist/babel-plugin-jsx-adopt/blob/c76850888c7fa4d4f04eb8b178f9ff2fa8f418c5/src/index.js#L143

stmt will be found in outer function (the one containing example), logic should be contained to the nearest function only, which in this care is the whats inside example