net: dsa: sja1105: allow XPCS to handle mdiodev lifetime

Put the mdiodev after xpcs_create() so that the XPCS driver can manage
the lifetime of the mdiodev its using.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>