cciss: factor out core of sendcmd_withirq() for use by SCSI error handling code

Factor the core of sendcmd_withirq out to provide a simpler interface
which provides access to full error information.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cca.cpqcorp.net>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>