iio:dac:max517.c: Use devm_iio_device_register()

Use devm_iio_device_register() to avoid remove function and
drop explicit call to iio_device_unregister().

Signed-off-by: Mugilraj Dhavachelvan <dmugil2000@gmail.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20210314175709.34301-1-dmugil2000@gmail.com


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