cciss: fix cciss_revalidate panic

If you delete a logical drive, and then run BLKRRPART (e.g. via fdisk)
on a logical drive which is "after" the deleted logical drive in the h->drv[]
array, then cciss_revalidate panics because it will access the null pointer
h->drv[x] when x hits the deleted drive.
Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

drivers/block/cciss.c

@@ -2834,6 +2834,8 @@ static int cciss_revalidate(struct gendisk *disk)
 	InquiryData_struct *inq_buff = NULL;
 
 	for (logvol = 0; logvol < CISS_MAX_LUN; logvol++) {
+		if (!h->drv[logvol])
+			continue
 		if (memcmp(h->drv[logvol]->LunID, drv->LunID,
 			sizeof(drv->LunID)) == 0) {
 			FOUND = 1;