mfd: retu: Add OF device ID table

mfd: retu: Add OF device ID table

The driver doesn't have a struct of_device_id table but supported devices
are registered via Device Trees. This is working on the assumption that a
I2C device registered via OF will always match a legacy I2C device ID and
that the MODALIAS reported will always be of the form i2c:<device>.

But this could change in the future so the correct approach is to have a
OF device ID table if the devices are registered via OF.

Signed-off-by: Javier Martinez Canillas <javier@dowhile0.org>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>