Fix NullPointerException on init of HdmiMhlController.

Change-Id: I2f79ce0ef3a368c2fcc8d047de2dcad914679e0c

services/core/java/com/android/server/hdmi/HdmiControlService.java

@@ -53,6 +53,7 @@ public final class HdmiControlService extends SystemService {
 
     @Override
     public void onStart() {
+        mIoThread.start();
         mCecController = HdmiCecController.create(this);
         if (mCecController != null) {
             mCecController.initializeLocalDevices(getContext().getResources()