I2O: cleanup - remove i2o_device_class

I2O devices reside on their own bus so there should be no reason
to also have i2c_device class that mirros i2o bus.
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>