net: fs_enet: fix reference counting for phy_node

Make sure that fs_enet_probe is left with a reference to the phy node.
In the presence of a phy handle this is already the case as
of_parse_phandle returns a reference. In the fixed phy case a call to
of_node_get is necessary. Otherwise the error path and remove function
drop a reference the driver isn't holding.

Fixes: bb74d9a4a87b ("fs_enet: 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>