Hook into Gravity Forms after form submission in order to save latitude/longitude in the format expected by the CMB Field Type: Google Maps plugin.

functions.php

<?php
/**
 * Save latitude/longitude for display in a CMB field
 *
 * @author Phil Wylie
 * @link http://link.from.pw/1ejMnDr
 */
function pw_save_latitude_longitude( $entry, $form ) {
	$latitude = $entry[3]; // where 3 is the field ID for latitude
	$longitude = $entry[4]; // where 4 is the field ID for longitude

	$location = array(
		'latitude' => $latitude,
		'longitude' => $longitude
	);

	update_post_meta( $entry['post_id'], 'location', $location ); // location is your CMB field ID
}
add_action( 'gform_after_submission_1', 'pw_save_latitude_longitude', 10, 2 ); // where 1 is the form ID