net: phy: mscc: improve vsc8514/8584_config_init consistency

All PHY read and write return values are checked for errors in
vsc8514_config_init and vsc8584_config_init, except for one. Fix this.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>