[SCSI] ses: fix hotplug with multiple devices and expanders

In a situation either with expanders or with multiple enclosure
devices, hot add doesn't always work.  This is because we try to find
a single enclosure device attached to the host.  Fix this by looping
over all enclosure devices attached to the host and also by making the
find loop recognise that the enclosure devices may be expander remote
(i.e. not parented by the host).

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>