net: phy: mscc: fix header defines and descriptions

Cosmetic commit fixing the MSCC PHY header defines and descriptions,
which were referring the to MSCC Ocelot MAC driver (see
drivers/net/ethernet/mscc/).

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>