fix(iobackend): missing header

src/io_backend/io_backend.c

@@ -125,7 +125,7 @@ int iob_config_from_args(struct args_options *args, struct iob_context *ctx)
         break;
 
     default:
-        return -1;
+        return IOB_ERROR_GENERIC;
     }
     return 0;
-}
+}