net: dsa: use of_for_each_phandle

The OF code provides a of_for_each_phandle() helper to iterate over
phandles. Use it instead of arbitrary iterating ourselves over the list
of phandles hanging to the "link" property of the port's device node.

The of_phandle_iterator_next() helper calls of_node_put() itself on
it.node. Thus We must only do it ourselves if we break the loop.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>