The trigger_handler gets called from the IRQ thread handler using
iio_trigger_poll_chained() which will only call the bottom half of the
pollfunc and therefore pf->timestamp will not get set.

Use instead the timestamp from the driver's private data which is always
set in the IRQ handler.

Fixes: 7c1d1677 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")
Link: https://lore.kernel.org/linux-iio/Y+6QoBLh1k82cJVN@carbian/Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Signed-off-by: Mehdi Djait <mehdi.djait.k@gmail.com>
Link: https://lore.kernel.org/r/20230218135111.90061-1-mehdi.djait.k@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>