iio: dac: ad5592r: destroy mutexes in detach paths

The locks used here are initialized but never released which causes
resource leaks with mutex debugging enabled. Add missing calls to
mutex_destroy() or use devres if applicable.

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-v2-1-4b36428f39cb@linaro.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>