When an I/O request failed, now we only return correct
value on scsi check condition. We should also have a
default errno such as -EIO in other case.

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Message-Id: <20200701105444.3226-2-xieyongji@bytedance.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>