net: mscc: ocelot: add missing of_node_put after calling of_get_child_by_name

of_node_put needs to be called when the device node which is got
from of_get_child_by_name finished using.
In both cases of success and failure, we need to release 'ports',
so clean up the code using goto.

fixes: a556c76a ("net: mscc: Add initial Ocelot switch support")
Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>