scsi: Assign cancel_io vector for scsi_disk_emulate_ops

Some emulated disk operations (MODE SELECT, UNMAP, WRITE SAME)
can trigger asynchronous I/Os.  Provide the cancel_io callback
to ensure that AIOCBs are properly cleaned up.
Signed-off-by: NEric Farman <farman@linux.vnet.ibm.com>
Cc: qemu-stable@nongnu.org
[Tweak commit message. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/scsi/scsi-disk.c

@@ -2306,6 +2306,7 @@ static const SCSIReqOps scsi_disk_emulate_reqops = {
     .send_command = scsi_disk_emulate_command,
     .read_data    = scsi_disk_emulate_read_data,
     .write_data   = scsi_disk_emulate_write_data,
+    .cancel_io    = scsi_cancel_io,
     .get_buf      = scsi_get_buf,
 };