staging: iio: tsl2x7x: no need to clear interrupt flag when getting lux

tsl2x7x_get_lux() does not need to clear the interrupt flag when
querying the ALS. The interrupt flag is cleared in
tsl2x7x_event_handler(). This patches removes the unnecessary code.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>