staging: iio: tsl2x7x: add missing error checks

The functions in_illuminance0_calibrate_store() and
in_illuminance0_lux_table_store() did not have complete error handling
in place. This patch adds the missing error handling.

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