sfc: fix addr_list_lock spinlock use before init

Reported by Nikolay Aleksandrov.  In efx_init_port() we call
 efx_mac_reconfigure() to work around a Falcon/A1 limitation, and this calls
 efx_{arch}_filter_sync_rx_mode(), which takes the addr_list_lock; but this
 lock is uninitialised, because we haven't called register_netdevice() yet.
So, in efx_farch_filter_sync_rx_mode(), check efx_dev_registered() before
 doing anything else.
The EF10 equivalent, efx_ef10_filter_sync_rx_mode(), already has the
 corresponding check.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Tested-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/farch.c

@@ -2933,6 +2933,9 @@ void efx_farch_filter_sync_rx_mode(struct efx_nic *efx)
 	u32 crc;
 	int bit;
 
+	if (!efx_dev_registered(efx))
+		return;
+
 	netif_addr_lock_bh(net_dev);
 
 	efx->unicast_filter = !(net_dev->flags & IFF_PROMISC);