hsi: Fix build regression due to netdev destructor fix.

> ../drivers/hsi/clients/ssi_protocol.c:1069:5: error: 'struct net_device' has no member named 'destructor'

Reported-by: Mark Brown <broonie@kernel.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/hsi/clients/ssi_protocol.c

@@ -1066,7 +1066,7 @@ static void ssip_pn_setup(struct net_device *dev)
 	dev->addr_len		= 1;
 	dev->tx_queue_len	= SSIP_TXQUEUE_LEN;
 
-	dev->destructor		= free_netdev;
+	dev->needs_free_netdev	= true;
 	dev->header_ops		= &phonet_header_ops;
 }