cgls: print the expressive error message we have

src/cgls/cgls.c

@@ -160,7 +160,7 @@ static int get_cgroup_root(char **ret) {
                         &error,
                         ret);
         if (r < 0)
-                return log_error_errno(r, "Failed to query unit control group path: %m");
+                return log_error_errno(r, "Failed to query unit control group path: %s", bus_error_message(&error, r));
 
         return 0;
 }