staging: unisys: Guard against task leakage

Its possible to overwrite the old task pointer in visornic_resume.  Add a
check to guard against that and a warning if we find that its already
running

Signed-off-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>