drm/i915: Make intel_get_pipe_from_connector atomic

Drive-by fixup while looking at all the connector_list walkers -
holding connection_mutex does actually _not_ give you locking to look
at the legacy drm_connector->encoder->crtc pointer chain. That one is
solely owned by the atomic commit workers. Instead we must inspect the
atomic state.
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170301095226.30584-4-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/intel_display.c

@@ -13889,15 +13889,14 @@ static int intel_crtc_init(struct drm_i915_private *dev_priv, enum pipe pipe)
 
 enum pipe intel_get_pipe_from_connector(struct intel_connector *connector)
 {
-	struct drm_encoder *encoder = connector->base.encoder;
 	struct drm_device *dev = connector->base.dev;
 
 	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
 
-	if (!encoder || WARN_ON(!encoder->crtc))
+	if (!connector->base.state->crtc)
 		return INVALID_PIPE;
 
-	return to_intel_crtc(encoder->crtc)->pipe;
+	return to_intel_crtc(connector->base.state->crtc)->pipe;
 }
 
 int intel_get_pipe_from_crtc_id(struct drm_device *dev, void *data,