Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I0ce850de85e0de6a5472dd142f738856142db9ec
diff --git a/libs/binder/IPermissionController.cpp b/libs/binder/IPermissionController.cpp
index 6bba996..674bddf 100644
--- a/libs/binder/IPermissionController.cpp
+++ b/libs/binder/IPermissionController.cpp
@@ -31,7 +31,7 @@
 class BpPermissionController : public BpInterface<IPermissionController>
 {
 public:
-    BpPermissionController(const sp<IBinder>& impl)
+    explicit BpPermissionController(const sp<IBinder>& impl)
         : BpInterface<IPermissionController>(impl)
     {
     }