fix(virtio/mmio): don't allow dead code

Author: mkroening

src/drivers/virtio/transport/mmio.rs

@@ -1,7 +1,6 @@
 //! A module containing all virtio specific pci functionality
 //!
 //! The module contains ...
-#![allow(dead_code)]
 
 #[cfg(feature = "console")]
 use alloc::boxed::Box;