staging: iio: tsl2x7x: correct 'Avoid CamelCase' warning from checkpatch

The statP and calP variables triggered an 'Avoid CamelCase' warning
from checkpatch.pl. This patch renames these variables to stat and cal
to fix this warning.

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