[SCSI] fix refcounting bug in scsi_get_host_dev

This patch (as1334) fixes a bug in scsi_get_host_dev().  It
incorrectly calls get_device() on the new device's target.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>