net: phy: at803x: remove config_init for AR9331

According to its datasheet, the internal PHY doesn't have debug
registers nor MMDs. Since config_init() only configures delays and
clocks and so on in these registers it won't be needed on this PHY.
Remove it.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>