binder_ndk: fix bugprone-unhandled-self-assignment

Bug: 162909698
Test: m checkbuild

Change-Id: I2a448282bef0a79aff62da70175e35d43da4699f
diff --git a/libs/binder/ndk/include_cpp/android/binder_auto_utils.h b/libs/binder/ndk/include_cpp/android/binder_auto_utils.h
index 8d60226..d9d9baf 100644
--- a/libs/binder/ndk/include_cpp/android/binder_auto_utils.h
+++ b/libs/binder/ndk/include_cpp/android/binder_auto_utils.h
@@ -74,6 +74,9 @@
      * ownership of that other object.
      */
     SpAIBinder& operator=(const SpAIBinder& other) {
+        if (this == &other) {
+            return *this;
+        }
         AIBinder_incStrong(other.mBinder);
         set(other.mBinder);
         return *this;