Fix `go vet` issues

Test: go vet ./...
Change-Id: Ifb936ccc5e2b5a2c3fcbbbcb54f680e2973ea1b3
diff --git a/android/namespace.go b/android/namespace.go
index 0230524..b027ceb 100644
--- a/android/namespace.go
+++ b/android/namespace.go
@@ -94,10 +94,8 @@
 }
 
 func NewNameResolver(namespaceExportFilter func(*Namespace) bool) *NameResolver {
-	namespacesByDir := sync.Map{}
-
 	r := &NameResolver{
-		namespacesByDir:       namespacesByDir,
+		namespacesByDir:       sync.Map{},
 		namespaceExportFilter: namespaceExportFilter,
 	}
 	r.rootNamespace = r.newNamespace(".")