Fix -Wunused-variable compiler warning

Test: presubmit
Change-Id: Ifd5f633a517d6dbd7344849a739acb32cb142296
diff --git a/services/incremental/IncrementalService.cpp b/services/incremental/IncrementalService.cpp
index 81a5472..a8e6f68 100644
--- a/services/incremental/IncrementalService.cpp
+++ b/services/incremental/IncrementalService.cpp
@@ -910,7 +910,7 @@
                                                constants().readLogsDisabledMarkerName),
                                     0777, idFromMetadata(metadata), {})) {
         //{.metadata = {metadata.data(), (IncFsSize)metadata.size()}})) {
-        LOG(ERROR) << "Failed to make marker file for storageId: " << storageId;
+        LOG(ERROR) << "Failed to make marker file for storageId: " << storageId << " err: " << -err;
         return;
     }