staging: iio: tsl2x7x: simplify tsl2x7x_clear_interrupts function

tsl2x7x_clear_interrupts() takes a reg argument but there are only
two callers to this function and both callers pass the same value.
Since this function was introduced, interrupts are now working
properly for this driver, and several unnecessary calls to
tsl2x7x_clear_interrupts() were removed. This patch removes the
tsl2x7x_clear_interrupts() function and replaces the two callers
with the i2c_smbus_write_byte() call instead.

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