get_the_ID is a WordPress core fuction in the global namespace, so you can’t make a second function called get_the_ID as it won’t know which one to use. You should just call get_the_ID() without writing a new function.
For your example code, you could do something like this:
<div>
<?php echo do_shortcode( '[svg-flag flag="' . get_post_meta( get_the_ID(), 'ozellikler_text', true ) . '"]' ); ?>
</div>