iio: imu: st_lsm6dsx: Fix wakeup source leaks on device unbind

Device can be unbound, so driver must also release memory for the wakeup
source.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250406-b4-device-wakeup-leak-iio-v1-3-2d7d322a4a93@linaro.org


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