Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I83bb2282249ecd4e39347b90f5fb53788e1fff5b
diff --git a/services/powermanager/IPowerManager.cpp b/services/powermanager/IPowerManager.cpp
index bff8719..ea3a831 100644
--- a/services/powermanager/IPowerManager.cpp
+++ b/services/powermanager/IPowerManager.cpp
@@ -30,7 +30,7 @@
 class BpPowerManager : public BpInterface<IPowerManager>
 {
 public:
-    BpPowerManager(const sp<IBinder>& impl)
+    explicit BpPowerManager(const sp<IBinder>& impl)
         : BpInterface<IPowerManager>(impl)
     {
     }