net: mscc: ocelot: omit error check from of_get_phy_mode

The commit 0c65b2b9 ("net: of_get_phy_mode: Change API to solve
int/unit warnings") updated the function of_get_phy_mode declaration.
Now it returns an error code and in case the node doesn't contain the
property 'phy-mode' or 'phy-connection-type' it returns -EINVAL and would
set the phy_interface_t to PHY_INTERFACE_MODE_NA.

Ocelot VSC7514 has 4 internal phys which have the phy interface
PHY_INTERFACE_MODE_NA. So because of_get_phy_mode would assign
PHY_INTERFACE_MODE_NA to phy_mode when there is an error, there is no need
to add the error check.

Updates for v2:
 - drop error check because of_get_phy_mode already assigns phy_interface
   to PHY_INTERFACE_MODE in case of error.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>