Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IAudioPolicyServiceClient.cpp b/media/libmedia/IAudioPolicyServiceClient.cpp
index 65cc7d6..c015d24 100644
--- a/media/libmedia/IAudioPolicyServiceClient.cpp
+++ b/media/libmedia/IAudioPolicyServiceClient.cpp
@@ -36,7 +36,7 @@
 class BpAudioPolicyServiceClient : public BpInterface<IAudioPolicyServiceClient>
 {
 public:
-    BpAudioPolicyServiceClient(const sp<IBinder>& impl)
+    explicit BpAudioPolicyServiceClient(const sp<IBinder>& impl)
         : BpInterface<IAudioPolicyServiceClient>(impl)
     {
     }