[PATCH 2/3] cciss: bug fix for BIG_PASS_THRU

Applications using CCISS_BIG_PASSTHRU complained that the data written
was zeros. The problem is that the buffer is being cleared after the
user copy, unless the user copy has failed... Correct that logic.

Signed-off-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: Jens Axboe <axboe@suse.de>