drm/i915: Remove crtc->config dereferences in intel_modeset_setup_hw_state

The CRTC is idle at this point, so we can dereference crtc->state safely.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
[mlankhorst: Keep dev_priv->drm in for_each_intel_crtc (Ville)]
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181011100457.8776-8-maarten.lankhorst@linux.intel.com