drm/i915: use intel_fb_obj() macros to assign gem objects

Use the macros makes the code cleaner and it also checks for a NULL fb.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_sprite.c

@@ -1032,8 +1032,7 @@ intel_check_sprite_plane(struct drm_plane *plane,
 	struct intel_crtc *intel_crtc = to_intel_crtc(state->crtc);
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	struct drm_framebuffer *fb = state->fb;
-	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
-	struct drm_i915_gem_object *obj = intel_fb->obj;
+	struct drm_i915_gem_object *obj = intel_fb_obj(fb);
 	int crtc_x, crtc_y;
 	unsigned int crtc_w, crtc_h;
 	uint32_t src_x, src_y, src_w, src_h;
@@ -1235,9 +1234,8 @@ intel_commit_sprite_plane(struct drm_plane *plane,
 	struct intel_plane *intel_plane = to_intel_plane(plane);
 	enum pipe pipe = intel_crtc->pipe;
 	struct drm_framebuffer *fb = state->fb;
-	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
-	struct drm_i915_gem_object *obj = intel_fb->obj;
-	struct drm_i915_gem_object *old_obj = intel_plane->obj;
+	struct drm_i915_gem_object *obj = intel_fb_obj(fb);
+	struct drm_i915_gem_object *old_obj = intel_fb_obj(plane->fb);
 	int crtc_x, crtc_y;
 	unsigned int crtc_w, crtc_h;
 	uint32_t src_x, src_y, src_w, src_h;