CameraBase: Don't return an sp<> by reference

If the server dies, the binder death callback clears out
the global camera service sp<>, and any current references to it
will become quite unhappy.

Test: Camera CTS passes
Bug: 31992879
Change-Id: I2966bed35d0319e3f26e3d4b1b8dc08006a22348
diff --git a/include/camera/CameraBase.h b/include/camera/CameraBase.h
index 0692a27..41f8621 100644
--- a/include/camera/CameraBase.h
+++ b/include/camera/CameraBase.h
@@ -115,7 +115,7 @@
     virtual void                     binderDied(const wp<IBinder>& who);
 
     // helper function to obtain camera service handle
-    static const sp<::android::hardware::ICameraService>& getCameraService();
+    static const sp<::android::hardware::ICameraService> getCameraService();
 
     sp<TCamUser>                     mCamera;
     status_t                         mStatus;