nvmet: Use PTR_ERR_OR_ZERO() in nvmet_init_discovery()

Simplify this function implementation by using a known function.

Generated by: scripts/coccinelle/api/ptr_ret.cocci
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/target/discovery.c

@@ -381,9 +381,7 @@ int __init nvmet_init_discovery(void)
 {
 	nvmet_disc_subsys =
 		nvmet_subsys_alloc(NVME_DISC_SUBSYS_NAME, NVME_NQN_DISC);
-	if (IS_ERR(nvmet_disc_subsys))
-		return PTR_ERR(nvmet_disc_subsys);
-	return 0;
+	return PTR_ERR_OR_ZERO(nvmet_disc_subsys);
 }
 
 void nvmet_exit_discovery(void)