drm/i915: Fix hw state verifier access to crtc->state.

We shouldn't inspect crtc->state, instead grab the crtc state.
At this point the hw state verifier should be able to run even if
crtc->state has been updated (which cannot currently happen).

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511082844.13965-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>