i2c: i2c-bcm-kona: Fix module build

Correct a typo that prevented the driver from being built as a module.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Tim Kryger <tim.kryger@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>