[PATCH] cciss: change cciss_open for consistency

Change our open to test for drv->heads like we do in other places in the
driver.  Mostly for consistency.

Signed-off-by: Mike Miller <mike.miller@hp.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>