scsi: annotate sdev_prefix_printk and scmd_printk as printf-like

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Bottomley <JBottomley@Parallels.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>