tuna: PowerHAL: Check that PowerHAL is successfully initialized

It doesn't make any sense to do something if PowerHAL
couldn't setup initial parameters successfully.

Cherry-picked and adjusted for tuna from
http://omapzoom.org/?p=device/ti/blaze_tablet.git;a=commit;h=5b250f0dbc8fa43f8ff9e45151730b5b733c5ed0

Change-Id: I4e87f6b7be53e52f21f02cc500c8a1096f70df5f