memstick: change to use __blk_end_request()

This patch converts memstick to use __blk_end_request() directly
so that end_{queued|dequeued}_request() can be removed.

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