staging: iio: tsl2x7x: correct IIO_EV_INFO_PERIOD values

The thresh periods assumed an integration time of 3ms. This patch adds
support for the correct integration time (2.72ms or 2.73ms). The code
had the ALS filter values as going up to 15, however the values actually
went up to 60 since the values scaled in increments of 5 once the
persistence value went above 3.

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