How to add Previous/Next links on single pages of custom post type in Genesis

Previous Next Post navigation in Genesis

/** Genesis Previous/Next Post Post Navigation */
add_action( 'genesis_after_entry', 'custom_prev_next_post_nav' );
function custom_prev_next_post_nav() {
if ( ! is_singular( 'portfolio' ) )  return;
	echo '<div id="prev-next">';
	previous_post_link( '<div class="prev-link"> %link</div>', '<span>&larr;</span>%title' );
	next_post_link( '<div class="next-link"> %link</div>', '%title<span>&rarr;</span>' );
	echo '</div><!-- .prev-next-navigation -->';
}