Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/camera/camera2/ICameraDeviceUser.cpp b/camera/camera2/ICameraDeviceUser.cpp
index 2a9fd2b..1aca242 100644
--- a/camera/camera2/ICameraDeviceUser.cpp
+++ b/camera/camera2/ICameraDeviceUser.cpp
@@ -69,7 +69,7 @@
 class BpCameraDeviceUser : public BpInterface<ICameraDeviceUser>
 {
 public:
-    BpCameraDeviceUser(const sp<IBinder>& impl)
+    explicit BpCameraDeviceUser(const sp<IBinder>& impl)
         : BpInterface<ICameraDeviceUser>(impl)
     {
     }