Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IAudioFlingerClient.cpp b/media/libmedia/IAudioFlingerClient.cpp
index 3429d36..343db41 100644
--- a/media/libmedia/IAudioFlingerClient.cpp
+++ b/media/libmedia/IAudioFlingerClient.cpp
@@ -34,7 +34,7 @@
 class BpAudioFlingerClient : public BpInterface<IAudioFlingerClient>
 {
 public:
-    BpAudioFlingerClient(const sp<IBinder>& impl)
+    explicit BpAudioFlingerClient(const sp<IBinder>& impl)
         : BpInterface<IAudioFlingerClient>(impl)
     {
     }