iio: ltc2983: Fix of_node refcounting

When returning or breaking early from a
`for_each_available_child_of_node()` loop, we need to explicitly call
`of_node_put()` on the child node to possibly release the node.

Fixes: f110f318 ("iio: temperature: Add support for LTC2983")
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200925091045.302-1-nuno.sa@analog.com


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