Override genesis site icon with jetpack site icon.

gistfile1.php

add_filter( 'genesis_pre_load_favicon', 'check_jetpack_site_icon' );
function check_jetpack_site_icon() {
	if (function_exists( 'jetpack_has_site_icon' ) && jetpack_has_site_icon()) {
		return jetpack_site_icon_url();
	}
	return false;
}