staging: iio: tsl2x7x: remove unused variables from tsl2x7x_get_lux()

tsl2x7x_get_lux() has a ch0lux and ch1lux variables that are not used
so this patch removes them.

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