staging: iio: tsl2x7x: put function definitions on a single line

The functions tsl2x7x_invoke_change() and tsl2x7x_prox_calculate() are
short enough that the return value and static declaration can be moved
onto the same line with the function name. This patch makes that change
to increase code readability.

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