net: phy: marvell10g: fix temperature sensor on 2110

Read the temperature sensor register from the correct location for the
88E2110 PHY. There is no enable/disable bit on 2110, so make
mv3310_hwmon_config() run on 88X3310 only.

Fixes: 62d01535 ("net: phy: marvell10g: add support for the 88x2110 PHY")
Cc: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>