sfc: make mem_bar a function rather than a constant

Support using BAR 0 on SFC9250, even though the driver doesn't bind to such
 devices yet.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index c0537ea..2b6599f 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -1154,7 +1154,7 @@ struct efx_udp_tunnel {
  */
 struct efx_nic_type {
 	bool is_vf;
-	unsigned int mem_bar;
+	unsigned int (*mem_bar)(struct efx_nic *efx);
 	unsigned int (*mem_map_size)(struct efx_nic *efx);
 	int (*probe)(struct efx_nic *efx);
 	void (*remove)(struct efx_nic *efx);