Fix google-explicit-constructor warnings in camera.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I61f9b5b2b6e13e0c6561327bc8dfe69c9cfc5ba5
diff --git a/camera/ndk/impl/ACameraDevice.h b/camera/ndk/impl/ACameraDevice.h
index 71e364d..051462b 100644
--- a/camera/ndk/impl/ACameraDevice.h
+++ b/camera/ndk/impl/ACameraDevice.h
@@ -65,7 +65,7 @@
     // Callbacks from camera service
     class ServiceCallback : public hardware::camera2::BnCameraDeviceCallbacks {
       public:
-        ServiceCallback(CameraDevice* device) : mDevice(device) {}
+        explicit ServiceCallback(CameraDevice* device) : mDevice(device) {}
         binder::Status onDeviceError(int32_t errorCode,
                            const CaptureResultExtras& resultExtras) override;
         binder::Status onDeviceIdle() override;