Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I0ce850de85e0de6a5472dd142f738856142db9ec
diff --git a/libs/binder/IBatteryStats.cpp b/libs/binder/IBatteryStats.cpp
index e32c628..ad1e69f 100644
--- a/libs/binder/IBatteryStats.cpp
+++ b/libs/binder/IBatteryStats.cpp
@@ -29,7 +29,7 @@
 class BpBatteryStats : public BpInterface<IBatteryStats>
 {
 public:
-    BpBatteryStats(const sp<IBinder>& impl)
+    explicit BpBatteryStats(const sp<IBinder>& impl)
         : BpInterface<IBatteryStats>(impl)
     {
     }