scsi: Fix trivial spelling

The word 'descriptor' is misspelled throughout the tree.

Fix it up accordingly:
    decriptors -> descriptors

Link: https://lore.kernel.org/r/20200609124610.3445662-7-kieran.bingham+renesas@ideasonboard.com
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>