i2c: nomadik: stop fetching the regulator

The regulator fetched by the Nomadik I2C driver is actually a
voltage domain regulator. Stop doing this in the driver and
let the power domain code handle any regulators, as discussed
on the list.

Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>