net: phy: at803x: fix PHY ID masks

Ever since its first commit 0ca7111a ("phy: add AT803x driver") the
PHY ID mask was set to 0xffffffef. It is unclear to me why this mask was
chosen in the first place. Both the AR8031/AR8033 and the AR8035
datasheets mention it is always the given value:
 - for AR8031/AR8033 its 0x004d/0xd074
 - for AR8035 its 0x004d/0xd072

Unfortunately, I don't have a datasheet for the AR8030. Therefore, we
leave its PHY ID mask untouched. For the PHYs mentioned before use the
handy PHY_ID_MATCH_EXACT() macro.

I've tried to contact the author of the initial commit, but received no
answer so far.

Cc: Matus Ujhelyi <ujhelyi.m@gmail.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>