mfd: Fix for DA9055 driver initialization

This patch clears all the events received while powering up DA9055.

While powering up DA9055, both power sequencer and gpio events are received.
These events remain uncleared after boot up, due to which further event handling
also fails. DA9055 has three event registers. The event register bits are set
to '1' on receiving an event. The events can be cleared on writing a '1' to
the set bit, which would then clear that bit to '0'. After applying this patch
we have a clean state after boot up.

Signed-off-by: Ankur Raina <Ankur.Raina@kpitcummins.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>