dev-virtio: VIO9P turns on diod verbose output with -d 1

Change-Id: I97e5762f4aca384068b87e22902e071fa3014ceb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22829
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>

src/dev/virtio/fs9p.cc

@@ -394,6 +394,7 @@ VirtIO9PDiod::startDiod()
 
         // Start diod
         execlp(diod, diod,
+               "-d", DTRACE(VIO9P) ? "1" : "0", // show debug output
                "-f", // start in foreground
                "-r", "3", // setup read FD
                "-w", "4", // setup write FD