net: phy: remove unneeded masking of PHY register read results

PHY registers are only 16 bits wide, therefore, if the read was
successful, there's no need to mask out the higher 16 bits.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>