detect-msg: cleanup error message

src/detect-msg.c

@@ -104,7 +104,7 @@ static int DetectMsgSetup (DetectEngineCtx *de_ctx, Signature *s, const char *ms
     }
 
     if (s->msg != NULL) {
-        SCLogError(SC_ERR_INVALID_RULE_ARGUMENT, "Duplicated 'msg:' keyword detected!");
+        SCLogError(SC_ERR_INVALID_SIGNATURE, "duplicated 'msg' keyword detected");
         goto error;
     }
     s->msg = SCStrdup(str);