Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IAudioPolicyService.cpp b/media/libmedia/IAudioPolicyService.cpp
index 76b5924..c993a5c 100644
--- a/media/libmedia/IAudioPolicyService.cpp
+++ b/media/libmedia/IAudioPolicyService.cpp
@@ -81,7 +81,7 @@
 class BpAudioPolicyService : public BpInterface<IAudioPolicyService>
 {
 public:
-    BpAudioPolicyService(const sp<IBinder>& impl)
+    explicit BpAudioPolicyService(const sp<IBinder>& impl)
         : BpInterface<IAudioPolicyService>(impl)
     {
     }