Fix unused parameter warning and enable -Werror.

Test: make -j60 android.hardware.gnss@1.0-impl still compiles
Change-Id: I98256f95b77944d514971be02dc4d4b445359541
diff --git a/gnss/1.0/default/GnssBatching.cpp b/gnss/1.0/default/GnssBatching.cpp
index 95c5e60..5e383e7 100644
--- a/gnss/1.0/default/GnssBatching.cpp
+++ b/gnss/1.0/default/GnssBatching.cpp
@@ -115,7 +115,7 @@
 }
 
 // this can just return success, because threads are now set up on demand in the jni layer
-int32_t GnssBatching::setThreadEventCb(ThreadEvent event) {
+int32_t GnssBatching::setThreadEventCb(ThreadEvent /*event*/) {
     return FLP_RESULT_SUCCESS;
 }