After the GPU has wedged we can't turn on the overlay anymore. Only mark
it as active if we succeed in allocating ring space. This prevents a
WARN (previous;y a BUG) during driver unload if we attempted to use the
overlay after the GPU had already wedged.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>