software/srslte: add missing output schema

It's empty because the instance does not publish anything at this point.

software/srslte/instance-srslte-output-schema.json

+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "description": "Values returned by srsLTE instanciation",
+  "properties": {},
+  "type": "object"
+}

software/srslte/software.cfg.json

@@ -8,7 +8,7 @@
       "software-type": "default",
       "description": "Default",
       "request": "instance-srslte-input-schema.json",
-      "response": "instance-srslte-schema.json",
+      "response": "instance-srslte-output-schema.json",
       "index": 1
     }
   }