The simplest solution is to use button group with 12345 buttons.
<?php
$ratingstar = get_field('checked');
?>
<span class="fa fa-star <?php if ($ratingstar >= 1) { echo 'checked';}?>"></span>
<span class="fa fa-star <?php if ($ratingstar >= 2) { echo 'checked';}?>"></span>
<span class="fa fa-star <?php if ($ratingstar >= 3) { echo 'checked';}?>"></span>
<span class="fa fa-star <?php if ($ratingstar >= 4) { echo 'checked';}?>"></span>
<span class="fa fa-star <?php if ($ratingstar == 5) { echo 'checked';}?>"></span>
