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: NTom Peng <tom_peng@usish.com>
Signed-off-by: NJack Wang <jack_wang@usish.com>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>