Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/soundtrigger/ISoundTriggerClient.cpp b/soundtrigger/ISoundTriggerClient.cpp
index e0d3add..1385631 100644
--- a/soundtrigger/ISoundTriggerClient.cpp
+++ b/soundtrigger/ISoundTriggerClient.cpp
@@ -35,7 +35,7 @@
 {
 
 public:
-    BpSoundTriggerClient(const sp<IBinder>& impl)
+    explicit BpSoundTriggerClient(const sp<IBinder>& impl)
         : BpInterface<ISoundTriggerClient>(impl)
     {
     }