dsa: fix for_each_child.cocci warnings

For_each_available_child_of_node should have of_node_put() before
return around line 423.

Generated by: scripts/coccinelle/iterators/for_each_child.cocci

CC: Alexander Lobakin <alobakin@pm.me>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Signed-off-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>