iscsi-target: fix error path in iscsi_target_init_module()

In iscsi_target_init_module() unwind transport protocol registration in case
that iscsit_load_discovery_tpg() failed.
Signed-off-by: NLino Sanfilippo <LinoSanfilippo@gmx.de>
Reviewed-by: NSagi Grimberg <sagig@mellanox.com>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -609,6 +609,7 @@ static int __init iscsi_target_init_module(void)
 
 	return ret;
 r2t_out:
+	iscsit_unregister_transport(&iscsi_target_transport);
 	kmem_cache_destroy(lio_r2t_cache);
 ooo_out:
 	kmem_cache_destroy(lio_ooo_cache);