net: phylink: propagate phy_attach_direct() return code

of_phy_attach() hides the return value of phy_attach_direct(), forcing
us to return a "generic" ENODEV error code that is indistinguishable
from the lack-of-phy-property case.

Switch to using of_phy_find_device() to find the PHY device, and then
propagating any phy_attach_direct() error back to the caller.

Link: https://lore.kernel.org/lkml/20191210113829.GT25745@shell.armlinux.org.uk


Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>