target: Add __exit annotation for module_exit functions

Inclues sbp_exit, fileio_module_exit, iblock_module_exit and
pscsi_module_exit.

Note: rd_module_exit() can not be annotated by __exit, becasue it is
called by target_core_init_configfs() which is annotated by __init.

Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 2bcfd79..37575a1 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -1178,7 +1178,7 @@
 	return transport_subsystem_register(&pscsi_template);
 }
 
-static void pscsi_module_exit(void)
+static void __exit pscsi_module_exit(void)
 {
 	transport_subsystem_release(&pscsi_template);
 }