i2c: designware-platform: Drop duplicate module information

The i2c-designware-platform module has duplicate module information
when CONFIG_I2C_DESIGNWARE_BAYTRAIL is set. It gets the information
from both i2c-designware-platdrv and i2c-designware-baytrail. The
latter is optional extra code which ends up in the same module so it
should not export module information.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>