scsi: scsi_dh_alua: Fix RCU annotations

This patch avoids that sparse complains about RCU pointer dereferences.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: tang.junhui <tang.junhui@zte.com.cn>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>