liquidio: using NULL instead of plain integer

Fix following warning:

drivers/net/ethernet/cavium/liquidio/cn23xx_pf_device.c:1453:35: warning: Using plain integer as NULL pointer
drivers/net/ethernet/cavium/liquidio/lio_main.c:2910:23: warning: Using plain integer as NULL pointer
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/liquidio/cn23xx_pf_device.c

@@ -1450,7 +1450,7 @@ void cn23xx_tell_vf_its_macaddr_changed(struct octeon_device *oct, int vfidx,
 		mbox_cmd.recv_len = 0;
 		mbox_cmd.recv_status = 0;
 		mbox_cmd.fn = NULL;
-		mbox_cmd.fn_arg = 0;
+		mbox_cmd.fn_arg = NULL;
 		ether_addr_copy(mbox_cmd.msg.s.params, mac);
 		mbox_cmd.q_no = vfidx * oct->sriov_info.rings_per_vf;
 		octeon_mbox_write(oct, &mbox_cmd);

drivers/net/ethernet/cavium/liquidio/lio_main.c

@@ -2907,7 +2907,7 @@ static int liquidio_set_vf_spoofchk(struct net_device *netdev, int vfidx,
 	nctrl.ncmd.s.param2 = enable;
 	nctrl.ncmd.s.more = 0;
 	nctrl.iq_no = lio->linfo.txpciq[0].s.q_no;
-	nctrl.cb_fn = 0;
+	nctrl.cb_fn = NULL;
 
 	retval = octnet_send_nic_ctrl_pkt(oct, &nctrl);