blk_end_request: changing cpqarray (take 4)

This patch converts cpqarray to use blk_end_request interfaces.
Related 'ok' arguments are converted to 'error'.

cpqarray is a little bit different from "normal" drivers.
cpqarray directly calls bio_endio() and disk_stat_add()
when completing request.  But those can be replaced with
__end_that_request_first().
After the replacement, request completion procedures of
those drivers become like the following:
    o end_that_request_first()
    o add_disk_randomness()
    o end_that_request_last()
This can be converted to __blk_end_request() by following
the rule (b) mentioned in the patch subject
"[PATCH 01/30] blk_end_request: add new request completion interface".

Cc: Mike Miller <mike.miller@hp.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>