net: gianfar: fix reference counting for phy_node

The line before the changed if condition is:

	priv->phy_node = of_parse_phandle(np, "phy-handle", 0);

. If this call succeeds priv->phy_node must not be overwritten in the if
block; otherwise the reference to the node returned by of_parse_phandle
is lost. So add a check that the if block isn't executed in this case.

Furthermore in the fixed phy case no reference is aquired for phy_node
resulting in an of_node_put without holding a reference. To fix that,
get a reference on the MAC dt node.

Fixes: be40364544bd ("gianfar: use the new fixed PHY helpers")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>