iio: dac: ad5770r: Put fwnode in error case during ->probe()

iio: dac: ad5770r: Put fwnode in error case during ->probe()

device_for_each_child_node() bumps a reference counting of a returned variable.
We have to balance it whenever we return to the caller.

Fixes: cbbb819837f6 ("iio: dac: ad5770r: Add AD5770R support")
Cc: Alexandru Tachici <alexandru.tachici@analog.com>
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210510095649.3302835-1-andy.shevchenko@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>