Use make_clickable()
function:
add_action( 'genesis_entry_footer', 'custom_comments_field' );
function custom_comments_field() {
if ( is_single() && genesis_get_custom_field('Comments link text') ) :
echo '<div class="comments-link">'. make_clickable( genesis_get_custom_field('Comments link text') ) .'</div>';
endif;
}
UPDATE:
In that case, try this:
add_action( 'genesis_entry_footer', 'custom_comments_field' );
function custom_comments_field() {
if ( is_single() && genesis_get_custom_field('Comments link text') ) :
global $post;
echo '<div class="comments-link"><a href="'. get_permalink( $post->ID ) .'">'. genesis_get_custom_field('Comments link text') .'</a></div>';
endif;
}