ARM: ux500: Stop passing ios_handler() as an MMCI power controlling call-back

This fixes a regression introduced during the v3.9 merge window.

Now MMCI on/off functionality is using the regulator framework
from the MMCI driver, if we provide the ios_handler call-back we
essentially duplicate functionality, which causes a large mess
and lots of booting issues.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>