Show error message when Android.mk files are found in directories in the deny list.

Bug: 318567881
Test: CIs
Test: add a Android.mk file in a blocked directory(e.g. cts/) and 'm nothing', an error message should be displayed and build process is stopped.
Change-Id: I3e1f63a13a20f77576b0e7424304a661f144df53
diff --git a/ui/build/finder.go b/ui/build/finder.go
index a114079..573df21 100644
--- a/ui/build/finder.go
+++ b/ui/build/finder.go
@@ -128,7 +128,7 @@
 
 	// Stop searching a subdirectory recursively after finding an Android.mk.
 	androidMks := f.FindFirstNamedAt(".", "Android.mk")
-	androidMks = blockAndroidMks(androidMks)
+	blockAndroidMks(ctx, androidMks)
 	err := dumpListToFile(ctx, config, androidMks, filepath.Join(dumpDir, "Android.mk.list"))
 	if err != nil {
 		ctx.Fatalf("Could not export module list: %v", err)