binder: fix google-explicit-constructor

Bug: 162909698
Test: m libbinder

Change-Id: I77ac3f7783ee0fe675c5ab42610eda25c4d51378
diff --git a/libs/binder/IServiceManager.cpp b/libs/binder/IServiceManager.cpp
index 6d728dc..35e642d 100644
--- a/libs/binder/IServiceManager.cpp
+++ b/libs/binder/IServiceManager.cpp
@@ -310,7 +310,7 @@
     // Simple RAII object to ensure a function call immediately before going out of scope
     class Defer {
     public:
-        Defer(std::function<void()>&& f) : mF(std::move(f)) {}
+        explicit Defer(std::function<void()>&& f) : mF(std::move(f)) {}
         ~Defer() { mF(); }
     private:
         std::function<void()> mF;