This patch adds check to bail out if device is already down when checking
for Tx hang subtask.

Change-ID: I3853fb7a6d11cb9a4c349b687cb25c15b19977a0
Signed-off-by: NAkeem G Abodunrin <akeem.g.abodunrin@intel.com>
Tested-by: NJim Young <james.m.young@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>