How to target specific user role?

get_role is just going to return information about the role. It isn’t going to tell you if the current user has that role. Use wp_get_current_user with a check something like this:

function subscriber_redirection() {
    global $redirect_to;
    $user = wp_get_current_user();
    if (in_array('subscriber',$user->roles)) {
        // user has subscriber role
        if ( !isset( $_GET['redirect_to'] ) ) {
            $redirect_to = get_option('siteurl');
        }
    }
}

I don’t know why you are using global $redirect_to; but never do anything with the variable.