This patch converts nbd to use blk_end_request interfaces.
Related 'uptodate' arguments are converted to 'error'.

Cc: Paul Clements <Paul.Clements@steeleye.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>