feat(config): Return missed error code

epicardium/modules/config.c

@@ -517,6 +517,7 @@ int epic_config_set_string(const char *key, const char *value_in)
 		);
 		if (nread == 0) {
 			LOG_DEBUG("card10.cfg", "could not read old value");
+			ret = -EIO;
 			goto complex_out;
 		}