net: phy: marvell10g: store temperature read method in chip strucutre

Now that we have a chip structure, we can store the temperature reading
method in this structure (OOP style).

Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>