Fix google-explicit-constructor warnings in libhardware

Bug: 28341362
Change-Id: I29a56734e54740e4b15fe2f6cacbbd867163ae79
Test: build with clang-tidy
diff --git a/tests/camera2/CameraModuleFixture.h b/tests/camera2/CameraModuleFixture.h
index 3a2df69..102fa6d 100644
--- a/tests/camera2/CameraModuleFixture.h
+++ b/tests/camera2/CameraModuleFixture.h
@@ -36,7 +36,7 @@
 template <bool InfoQuirk = false>
 struct CameraModuleFixture {
 
-    CameraModuleFixture(int CameraID = -1) {
+    explicit CameraModuleFixture(int CameraID = -1) {
         TEST_EXTENSION_FORKING_CONSTRUCTOR;
 
         mCameraID = CameraID;