net: ethernet: ti: davinci_emac: fix device reference leak

Make sure to drop the references taken by bus_find_device() before
returning from emac_dev_open().

Note that phy_connect still takes a reference to the phy device.

Fixes: 5d69e007 ("net: davinci_emac: switch to new mdio")
Cc: Mugunthan V N <mugunthanvnm@ti.com>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>