i2c: i801: Remove usage of I2C_CLASS_SPD

Only remaining client driver supporting I2C_CLASS_SPD is jc42. This
type of thermal sensor can be found on several DDR3/DDR4 modules.
i2c_register_spd() instantiates also such thermal sensor i2c devices.
Since 893fef0b ("i2c: i801: Call i2c_register_spd for muxed child
segments") i2c_register_spd() is called also for the remaining use case,
systems with muxed SMBUS segments for SPD EEPROMs.
Therefore I2C_CLASS_SPD class-based instantiation isn't needed any longer
in this driver, so remove it.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>