Fix google-explicit-constructor warnings in libhardware

Bug: 28341362
Change-Id: I29a56734e54740e4b15fe2f6cacbbd867163ae79
Test: build with clang-tidy
diff --git a/modules/camera/ExampleCamera.h b/modules/camera/ExampleCamera.h
index 45c4a94..44eac76 100644
--- a/modules/camera/ExampleCamera.h
+++ b/modules/camera/ExampleCamera.h
@@ -27,7 +27,7 @@
 // metadata and logic about that device.
 class ExampleCamera : public Camera {
     public:
-        ExampleCamera(int id);
+        explicit ExampleCamera(int id);
         ~ExampleCamera();
 
     private: