cciss: factor out core of sendcmd() for a more sane interface

Factor out the core of sendcmd() to provide a simpler interface which
exposes all the error information to the caller and make the original
sendcmd use this new function.  Rationale: The SCSI error handling
routines need to send commands with interrupts turned off, but they also
need access to the full error information.

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