Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IEffect.cpp b/media/libmedia/IEffect.cpp
index faf5795..115ca75 100644
--- a/media/libmedia/IEffect.cpp
+++ b/media/libmedia/IEffect.cpp
@@ -36,7 +36,7 @@
 class BpEffect: public BpInterface<IEffect>
 {
 public:
-    BpEffect(const sp<IBinder>& impl)
+    explicit BpEffect(const sp<IBinder>& impl)
         : BpInterface<IEffect>(impl)
     {
     }