contrib/fs-idmap: Check exactly 2 args are received

If more args are passed, let's just throw an error.

Signed-off-by: Rodrigo Campos <rodrigoca@microsoft.com>

contrib/cmd/fs-idmap/fs-idmap.go

@@ -11,7 +11,7 @@ import (
 )
 
 func main() {
-	if len(os.Args) < 2 {
+	if len(os.Args) != 2 {
 		log.Fatalf("usage: %s path_to_mount_set_attr", os.Args[0])
 	}