regulator: kryo-regulator: initialize default PM notifier return value

The kryo regulator driver receieves PM notifications when the
device enters various low power modes. However, the CPU PM
callback processes notifications corresponding only to M3 LPM
and returns otherwise. Assign NOTIFY_OK as the default return
code for this callback so that it is the value returned to
the LPM framework for notifications the driver does not
process.

Change-Id: I0edab1114ec143565f1487c37daebfc65fe67221
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>