ahci: clear aiocb in ncq_cb

Similar to existing fixes for IDE (87ac25fd) and ATAPI (7f951b2d), the
AIOCB must be cleared in the callback. Otherwise, we may accidentally
try to reset a dangling pointer in bdrv_aio_cancel() from a port reset.
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1474575040-32079-2-git-send-email-jsnow@redhat.com
Signed-off-by: NJohn Snow <jsnow@redhat.com>
(cherry picked from commit df403bc5)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

hw/ide/ahci.c

@@ -948,6 +948,7 @@ static void ncq_cb(void *opaque, int ret)
     NCQTransferState *ncq_tfs = (NCQTransferState *)opaque;
     IDEState *ide_state = &ncq_tfs->drive->port.ifs[0];
 
+    ncq_tfs->aiocb = NULL;
     if (ret == -ECANCELED) {
         return;
     }