staging: iio: tsl2x7x: rename power defines to improve code readability

The LED power defines are named like TSL2X7X_mAXXX. Rename these values
to TSL2X7X_XXX_mA to improve code readability.

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