SensorDeviceUtils: do not create sp(this) in constructor.

This may cause refcount problems as stated in RefBase
document. Do this in HidlServiceRegistrationWaiter::onFirstRef
instead.

Test: boots multiple times
Bug: 68765551
Change-Id: Iae2589f7e003cb8d44fe6ca43f1342b89125f763
diff --git a/services/sensorservice/SensorDeviceUtils.cpp b/services/sensorservice/SensorDeviceUtils.cpp
index 30de63f..dbafffe 100644
--- a/services/sensorservice/SensorDeviceUtils.cpp
+++ b/services/sensorservice/SensorDeviceUtils.cpp
@@ -29,6 +29,11 @@
 namespace SensorDeviceUtils {
 
 HidlServiceRegistrationWaiter::HidlServiceRegistrationWaiter() {
+}
+
+void HidlServiceRegistrationWaiter::onFirstRef() {
+    // Creating sp<...>(this) in the constructor should be avoided, hence
+    // registerForNotifications is called in onFirstRef callback.
     mRegistered = ISensors::registerForNotifications("default", this);
 }