scx200_i2c: Add missing class parameter

The scx200_i2c driver is missing the .class parameter, which means no
i2c drivers are willing to probe for devices on the bus and attach to
them.

Signed-off-by: Len Sorensen <lsorense@csclub.uwaterloo.ca>
Signed-off-by: Jean Delvare <khali@linux-fr.org>