net: dsa: lantiq_gswip: Fix refcount leak in gswip_gphy_fw_list

Every iteration of for_each_available_child_of_node() decrements
the reference count of the previous node.
when breaking early from a for_each_available_child_of_node() loop,
we need to explicitly call of_node_put() on the gphy_fw_np.
Add missing of_node_put() to avoid refcount leak.

Fixes: 14fceff4

 ("net: dsa: Add Lantiq / Intel DSA driver for vrx200")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20220605072335.11257-1-linmq006@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>