Document return value of AServiceManager_openDeclaredPassthroughHal

Bug: 326096214
Test: n/a (comments modified)
Change-Id: I555cabe0db815a936c4ee50799a30fb0d452ab65
diff --git a/libs/binder/ndk/include_platform/android/binder_manager.h b/libs/binder/ndk/include_platform/android/binder_manager.h
index b34b30d..a905dff 100644
--- a/libs/binder/ndk/include_platform/android/binder_manager.h
+++ b/libs/binder/ndk/include_platform/android/binder_manager.h
@@ -248,6 +248,8 @@
  * \param instance identifier of the passthrough service (e.g. "mapper")
  * \param instance identifier of the implemenatation (e.g. "default")
  * \param flag passed to dlopen()
+ *
+ * \return the result of dlopen of the specified HAL
  */
 void* AServiceManager_openDeclaredPassthroughHal(const char* interface, const char* instance,
                                                  int flag)