mfd: stw481x: Export I2C module alias information

The I2C core always reports the MODALIAS uevent as "i2c:<client name"
regardless if the driver was matched using the I2C id_table or the
of_match_table. So the driver needs to export the I2C table and this
be built into the module or udev won't have the necessary information
to auto load the correct module when the device is added.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>