drivers: net: cpsw: use of_phy_connect() in fixed-link case

If a fixed-link DT subnode is used, the phy_device was looked up so
that a PHY ID string could be constructed and passed to phy_connect().
This is not necessary, as the device_node can be passed directly to
of_phy_connect() instead. This reuses the same codepath as if the
phy-handle DT property was used.

Signed-off-by: David Rivshin <drivshin@allworx.com>
Tested-by: Nicolas Chauvet <kwizart@gmail.com>
Tested-by: Andrew Goodbody <andrew.goodbody@cambrionix.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>