net: lan966x: add missing fwnode_handle_put() for ports node

Since the "ethernet-ports" node is retrieved using
device_get_named_child_node(), it should be release after using it. Add
missing fwnode_handle_put() and move the code that retrieved the node
from device-tree to avoid complicated handling in case of error.

Fixes: db8bcaad

 ("net: lan966x: add the basic lan966x driver")
Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://lore.kernel.org/r/20230112161311.495124-1-clement.leger@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>