iscsi-target: Fix tfc_tpg_auth_cit configfs length overflow

This patch fixes another potential buffer overflow while processing
iscsi_node_auth input for configfs attributes in v3.11 for-next
TPG tfc_tpg_auth_cit context.
Reported-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_configfs.c

@@ -1081,7 +1081,7 @@ static ssize_t __iscsi_##prefix##_store_##name(					\
 	if (!capable(CAP_SYS_ADMIN))						\
 		return -EPERM;							\
 										\
-	snprintf(auth->name, PAGE_SIZE, "%s", page);				\
+	snprintf(auth->name, sizeof(auth->name), "%s", page);			\
 	if (!(strncmp("NULL", auth->name, 4)))					\
 		auth->naf_flags &= ~flags;					\
 	else									\