[SCSI] libsas: do not set res = 0 in sas_ex_discover_dev()

We should not set res to 0 in function sas_ex_discover_dev  in order to let
it discover it further when wide port hotplug in .

Signed-off-by: Tom Peng <tom_peng@usish.com>
Signed-off-by: Jack Wang <jack_wang@usish.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/libsas/sas_expander.c

@@ -960,7 +960,6 @@ static int sas_ex_discover_dev(struct domain_device *dev, int phy_id)
 
 			}
 		}
-		res = 0;
 	}
 
 	return res;