Reset firmware when inference cancellation fails

If an inference fails to be cancelled and it is still in a pending
state, reset the whole firmware.  Indeed the assumption is that
something is at fault on the firmware side and it is not progressing.

Change-Id: I2f568b2167d86cda3cb96a5e83551b018f5fc55d
diff --git a/kernel/ethosu_mailbox.h b/kernel/ethosu_mailbox.h
index 7af0c47..07276f6 100644
--- a/kernel/ethosu_mailbox.h
+++ b/kernel/ethosu_mailbox.h
@@ -138,9 +138,8 @@
  *
  * Call resend() callback on all messages in pending list.
  *
- * Return: 0 on success, else error code.
  */
-int ethosu_mailbox_resend(struct ethosu_mailbox *mbox);
+void ethosu_mailbox_resend(struct ethosu_mailbox *mbox);
 
 /**
  * ethosu_mailbox_reset() - Reset to end of queue