net: phy: clean up get_phy_c22_id() invalid ID handling

Move the ID check from get_phy_device() into get_phy_c22_id(), which
simplifies get_phy_device(). The ID reading functions are now
responsible for indicating whether they found a PHY or not via their
return code - they must return -ENODEV when a PHY is not present.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>