sys: fix memory leak in packagelist

Fixes commit 4e483312b0.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

sys.c

@@ -226,6 +226,7 @@ procstr:
 
 	blobmsg_close_table(&buf, tbl);
 	ubus_send_reply(ctx, req, buf.head);
+	blob_buf_free(&buf);
 	fclose(f);
 
 	return 0;