iio: adc: ti-ads8688: fix timestamp is not updated in buffer

commit e6d12298310fa1dc11f1d747e05b168016057fdd upstream.

When using the hrtimer iio trigger timestamp isn't updated.
If we use iio_get_time_ns it is updated correctly.

Fixes: 2a86487786b5c ("iio: adc: ti-ads8688: add trigger and buffer support")
Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/adc/ti-ads8688.c

@@ -397,7 +397,7 @@ static irqreturn_t ads8688_trigger_handler(int irq, void *p)
 	}
 
 	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
-			pf->timestamp);
+			iio_get_time_ns(indio_dev));
 
 	iio_trigger_notify_done(indio_dev->trig);