Otherwise we end up tearing down fences when e.g. the client quits
way too early. Might or might not fix a fence pin_count BUG Ville has
reported.
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>