Change stmmac_mdio_reset() to use device_property_read_u32_array()
instead of of_property_read_u32_array().

This is meant as a cleanup because we can drop the struct device_node
variable. Also it will make it easier to get rid of struct
stmmac_mdio_bus_data (or at least make it private) in the future because
non-OF platforms can now pass the reset delays as device properties.

No functional changes (neither for OF platforms nor for ones that are
not using OF, because the modified code is still contained in an "if
(priv->device->of_node)").
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>