drm/i915: Do not dereference NULL crtc or fb until after checking

Fixes regression from
commit 4906557
Author: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Date:   Thu Jul 11 18:45:05 2013 -0300

    drm/i915: Hook PSR functionality

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67526
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -1545,12 +1545,21 @@ static bool intel_edp_psr_match_conditions(struct intel_dp *intel_dp)
 		return false;
 	}
 
+	crtc = dig_port->base.base.crtc;
+	if (crtc == NULL) {
+		DRM_DEBUG_KMS("crtc not active for PSR\n");
+		dev_priv->no_psr_reason = PSR_CRTC_NOT_ACTIVE;
+		return false;
+	}
+
+	intel_crtc = to_intel_crtc(crtc);
 	if (!intel_crtc->active || !crtc->fb || !crtc->mode.clock) {
 		DRM_DEBUG_KMS("crtc not active for PSR\n");
 		dev_priv->no_psr_reason = PSR_CRTC_NOT_ACTIVE;
 		return false;
 	}
 
+	obj = to_intel_framebuffer(crtc->fb)->obj;
 	if (obj->tiling_mode != I915_TILING_X ||
 	    obj->fence_reg == I915_FENCE_REG_NONE) {
 		DRM_DEBUG_KMS("PSR condition failed: fb not tiled or fenced\n");