net/fsl: Remove leftover definition in xgmac_mdio

commit 26eee021 ("net/fsl: fix a bug in xgmac_mdio") fixed a bug in
the QorIQ mdio driver but left the (now unused) incorrect bit definition
for MDIO_DATA_BSY in the code. This commit removes it.

Signed-off-by: Markus Koch <markus@notsyncing.net>
Signed-off-by: David S. Miller <davem@davemloft.net>