cciss: simplify interface of sendcmd() and sendcmd_withirq()

Simplify interfaces of sendcmd() and sendcmd_withirq() so that they
provide only one way to address commands instead of three ways.

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