Use a timer in SensorReader

Since we know what time the next iteration should occur at,
it makes more sense to set a timer for that time instead of
modifying the PhasedLoop's offset.

Change-Id: Iddacb4726ea7278d910ba15e7780ebcad76b7858
Signed-off-by: milind-u <milind.upadhyay@gmail.com>
diff --git a/aos/events/event_loop.h b/aos/events/event_loop.h
index 8ef8d57..1000703 100644
--- a/aos/events/event_loop.h
+++ b/aos/events/event_loop.h
@@ -586,6 +586,8 @@
 
   // Creates a timer that executes callback when the timer expires
   // Returns a TimerHandle for configuration of the timer
+  // TODO(milind): callback should take the number of cycles elapsed as a
+  // parameter.
   virtual TimerHandler *AddTimer(::std::function<void()> callback) = 0;
 
   // Creates a timer that executes callback periodically at the specified