mfd: arizona: Request parent IRQ before we request child IRQs

Currently the driver requests the boot done and control interface IRQs
before it has requested its own IRQ line. This can cause problems on
edge triggered IRQ systems as if an edge occurs before the parent IRQ is
enabled it will be missed. Whilst we are changing the error handling
remove an unused label as well.

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