net: phy: at803x: Don't set gbit features for the AR8030 phy

The 8030 is only a "RMII Fast Ethernet PHY", thus it must not have the
SUPPORTED_1000* bits set.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>