Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I0ce850de85e0de6a5472dd142f738856142db9ec
diff --git a/libs/gui/IProducerListener.cpp b/libs/gui/IProducerListener.cpp
index 81adc95..9d18ea2 100644
--- a/libs/gui/IProducerListener.cpp
+++ b/libs/gui/IProducerListener.cpp
@@ -27,7 +27,7 @@
 class BpProducerListener : public BpInterface<IProducerListener>
 {
 public:
-    BpProducerListener(const sp<IBinder>& impl)
+    explicit BpProducerListener(const sp<IBinder>& impl)
         : BpInterface<IProducerListener>(impl) {}
 
     virtual ~BpProducerListener();