stmmac: move driver data setting into stmmac_dvr_probe

Move setting of driver data into stmmac_dvr_probe so the
other probe functions don't have to. This will help to
simplify the other probe functions later.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>