platform/chrome: cros_ec_sensorhub: Fix EC timestamp overflow

EC is using 32 bit timestamps (us), and before converting it to 64bit
they were not casted, so it would overflow every 4s.
Regular overflow every ~70 minutes was not taken into account either.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

drivers/platform/chrome/cros_ec_sensorhub_ring.c

@@ -419,9 +419,7 @@ cros_ec_sensor_ring_process_event(struct cros_ec_sensorhub *sensorhub,
 			 * Disable filtering since we might add more jitter
 			 * if b is in a random point in time.
 			 */
-			new_timestamp = fifo_timestamp -
-					fifo_info->timestamp  * 1000 +
-					in->timestamp * 1000;
+			new_timestamp = c - b * 1000 + a * 1000;
 			/*
 			 * The timestamp can be stale if we had to use the fifo
 			 * info timestamp.