net: cavium: For Kconfig THUNDER_NIC_BGX, select MDIO_THUNDER.

Previously we selected MDIO_OCTEON, which after creating the Thunder
specific MDIO bus driver is much less useful.
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/Kconfig

@@ -35,7 +35,7 @@ config	THUNDER_NIC_BGX
 	tristate "Thunder MAC interface driver (BGX)"
 	depends on 64BIT
 	select PHYLIB
-	select MDIO_OCTEON
+	select MDIO_THUNDER
 	---help---
 	  This driver supports programming and controlling of MAC
 	  interface from NIC physical function driver.