qla2xxx: Use d_id instead of s_id for more clarity

Updated code with d_id from s_id for better readability and
clarity.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
[ bvanassche: fixed spelling of patch description ]
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>

Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>