Using the media library for theme customization

I figured this out. For anyone facing the same issue, I ended up using this code instead:

function hi_customization_options( $wp_customize ) {
    $wp_customize->add_section(
        'landing_page_image',
        array(
            'title' => 'Landing Page Image',
            'priority' => 35,
        )
    );

    $wp_customize->add_setting(
        'lp-image_selector',
        array(
            'default' => '',
        )
    );

    $wp_customize->add_setting( 'img-upload' );

    $wp_customize->add_control(
        new WP_Customize_Image_Control(
            $wp_customize,
            'lp-image_selector',
            array(
                'label' => 'Landing Page Image',
                'section' => 'landing_page_image',
                'settings' => 'img-upload'
            )
        )
    );
}
add_action( 'customize_register', 'hi_customization_options' );