iio: adc: stm32-adc: Fix of_node_put() issue in stm32-adc

iio: adc: stm32-adc: Fix of_node_put() issue in stm32-adc

Fix following coccicheck warning:
./drivers/iio/adc/stm32-adc.c:2014:1-33: WARNING: Function
for_each_available_child_of_node should have of_node_put() before return.

Early exits from for_each_available_child_of_node should decrement the
node reference counter. Replace return by goto here.

Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Link: https://lore.kernel.org/r/20211021121826.6339-1-wanjiabing@vivo.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>