drm/i915: Skip GPU wait for scanout pin while wedged

Failing to pin a scanout buffer will most likely lead to a black
screen, so if the GPU is wedged, then just let the pin happen and hope
that things work out OK.

v2: Just ignore any error from i915_gem_object_wait_rendering, as
suggested by Chris Wilson

Signed-off-by: Keith Packard <keithp@keithp.com>