mfd: arizona: Disable DCVDD before we destroy the MFD

As DCVDD is probably supplied by a child of the MFD device move its
disable to before we destroy the MFD children as the regulator likely
won't exist after that.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>