drm/i915: Wake up waiters after setting the WEDGED bit

After setting the WEDGED bit, make sure that we do wake up waiters as
they may not be waiting for a request completion yet, just for its
execution.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-9-chris@chris-wilson.co.uk
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>