Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I0ce850de85e0de6a5472dd142f738856142db9ec
diff --git a/libs/binder/IAppOpsCallback.cpp b/libs/binder/IAppOpsCallback.cpp
index 2aaf566..f9ec593 100644
--- a/libs/binder/IAppOpsCallback.cpp
+++ b/libs/binder/IAppOpsCallback.cpp
@@ -31,7 +31,7 @@
 class BpAppOpsCallback : public BpInterface<IAppOpsCallback>
 {
 public:
-    BpAppOpsCallback(const sp<IBinder>& impl)
+    explicit BpAppOpsCallback(const sp<IBinder>& impl)
         : BpInterface<IAppOpsCallback>(impl)
     {
     }