[SCSI] libsas: don't mark expanders as gone when a child device is removed

Commit 56dd2c06

 "[SCSI] libsas: Don't issue commands to devices that
have been hot-removed" marked the parent device of an end-device as gone
when all the phys to the end device have been deleted.

The expander device is still present until its parent is removed.  This
is a benign change until the smp_execute_task() path is taught to check
->gone.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>