iio: st_sensors: fix typo in comment

s/timetamping/timestamping/

Cc: trivial@kernel.org
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.kernel.org/r/20210121153945.5499-1-a.fatoum@pengutronix.de


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>