net: dsa: fix a leaked reference by adding missing of_node_put

The call to of_parse_phandle returns a node pointer with refcount
incremented thus it must be explicitly decremented after the last
usage.

Detected by coccinelle with the following warnings:
./net/dsa/port.c:294:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 284, but without a corresponding object release within this function.
./net/dsa/dsa2.c:627:3-9: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 618, but without a corresponding object release within this function.
./net/dsa/dsa2.c:630:3-9: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 618, but without a corresponding object release within this function.
./net/dsa/dsa2.c:636:3-9: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 618, but without a corresponding object release within this function.
./net/dsa/dsa2.c:639:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 618, but without a corresponding object release within this function.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Vivien Didelot <vivien.didelot@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Vivien Didelot <vivien.didelot@gmail.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>