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 <[e-mail]>
Tested-by: Nikolay Aleksandrov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/sfc/farch.c

···
 	u32 crc;
 	int bit;
 
+	if (!efx_dev_registered(efx))
+		return;
+
 	netif_addr_lock_bh(net_dev);
 
 	efx->unicast_filter = !(net_dev->flags & IFF_PROMISC);