staging: iio: ad2s1200: Use devm_* APIs

devm_* APIs are device managed and make code simpler.
This patch also fixes the missing gpio_free call in remove.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Graff Yang <graff.yang@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
1 file changed