mfd: arizona: Remove unneded ret variable

The ret variable is not needed since is not used in the
function. Remove the variable and just return 0 instead.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>