cleanup: add _free on error path

Just like with failing allocation above also _free(dev).

TODO: rework this to always use mempool and drop unneeded
comlexity we have in this function.

lib/device/dev-cache.c

@@ -115,6 +115,7 @@ struct device *dev_create_file(const char *filename, struct device *dev,
 			}
 			if (!(alias->str = _strdup(filename))) {
 				log_error("filename strdup failed");
+				_free(dev);
 				return NULL;
 			}
 		}