Vibrator: clarify the API

Put stronger requirements on the vibrator API:
 - vibratorOn must not be called if the vibrator is already called (requirement
         on the caller);
 - vibratorOff must cancel any ongoing vibration (requirement on the callee).

Change-Id: Ic2fcd29903bf5a11a19c731de355d19c06c4e0e2
Signed-off-by: David Wagner <david.wagner@intel.com>
1 file changed