Fix google-explicit-constructor warnings in libhardware

Bug: 28341362
Change-Id: I29a56734e54740e4b15fe2f6cacbbd867163ae79
Test: build with clang-tidy
diff --git a/modules/sensors/SensorEventQueue.h b/modules/sensors/SensorEventQueue.h
index 11e1f41..9778e93 100644
--- a/modules/sensors/SensorEventQueue.h
+++ b/modules/sensors/SensorEventQueue.h
@@ -38,7 +38,7 @@
     pthread_cond_t mSpaceAvailableCondition;
 
 public:
-    SensorEventQueue(int capacity);
+    explicit SensorEventQueue(int capacity);
     ~SensorEventQueue();
 
     // Returns length of region, between zero and min(capacity, requestedLength). If there is any