target: Drop unnecessary core_tpg_register TFO parameter

This patch drops unnecessary target_core_fabric_ops parameter usage
for core_tpg_register() during fabric driver TFO->fabric_make_tpg()
se_portal_group creation callback execution.

Instead, use the existing se_wwn->wwn_tf->tf_ops pointer to ensure
fabric driver is really using the same TFO provided at module_init
time.

Also go ahead and drop the forward TFO declarations tree-wide, and
handling the special case for iscsi-target discovery TPG.

Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/loopback/tcm_loop.c b/drivers/target/loopback/tcm_loop.c
index b0c1761..bd9d11a 100644
--- a/drivers/target/loopback/tcm_loop.c
+++ b/drivers/target/loopback/tcm_loop.c
@@ -40,8 +40,6 @@
 
 #define to_tcm_loop_hba(hba)	container_of(hba, struct tcm_loop_hba, dev)
 
-static const struct target_core_fabric_ops loop_ops;
-
 static struct workqueue_struct *tcm_loop_workqueue;
 static struct kmem_cache *tcm_loop_cmd_cache;
 
@@ -1081,8 +1079,7 @@
 	/*
 	 * Register the tl_tpg as a emulated SAS TCM Target Endpoint
 	 */
-	ret = core_tpg_register(&loop_ops, wwn, &tl_tpg->tl_se_tpg,
-				tl_hba->tl_proto_id);
+	ret = core_tpg_register(wwn, &tl_tpg->tl_se_tpg, tl_hba->tl_proto_id);
 	if (ret < 0)
 		return ERR_PTR(-ENOMEM);