xen-scsiback: Fix compile warning for 64-bit LUN

drivers/xen/xen-scsiback.c: In function ‘scsiback_add_translation_entry’:
drivers/xen/xen-scsiback.c:911:3: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘long long unsigned int’ [-Wformat]
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/xen/xen-scsiback.c

@@ -908,7 +908,7 @@ static int scsiback_add_translation_entry(struct vscsibk_info *info,
 	mutex_unlock(&scsiback_mutex);
 
 	if (!tpg) {
-		pr_err("%s:%d %s\n", phy, unpacked_lun, error);
+		pr_err("%s:%llu %s\n", phy, unpacked_lun, error);
 		return -ENODEV;
 	}