iscsi: return -EIO when sense fields are meaningless

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>

block/iscsi.c

@@ -241,9 +241,11 @@ iscsi_co_generic_cb(struct iscsi_context *iscsi, int status,
 
     iTask->status = status;
     iTask->do_retry = 0;
+    iTask->err_code = 0;
     iTask->task = task;
 
     if (status != SCSI_STATUS_GOOD) {
+        iTask->err_code = -EIO;
         if (iTask->retries++ < ISCSI_CMD_RETRIES) {
             if (status == SCSI_STATUS_BUSY ||
                 status == SCSI_STATUS_TIMEOUT ||