iio: dac: ad5592r: use lock guards

iio: dac: ad5592r: use lock guards

Use lock guards from linux/cleanup.h to simplify the code and remove
some labels.

Note that we need to initialize some variables even though it's not
technically required as scoped_guards() are implemented as for loops.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250409-gpiochip-set-rv-iio-v2-2-4b36428f39cb@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>