drm/i915/selftests: Skip making an object busy if the GPU is wedged

If the GPU is wedged, we cannot make the object busy as trying to
submit a request will generate -EIO. Skip to the end of the test.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180706065332.15214-4-chris@chris-wilson.co.uk