drm/mode: introduce wrapper to read framebuffer refcount.

Avoids drivers knowing where the kref is stored.

[airlied: add kerneldoc]
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 4499b12..158bdca 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -612,7 +612,7 @@
 	 * in-use fb with fb-id == 0. Userspace is allowed to shoot its own foot
 	 * in this manner.
 	 */
-	if (atomic_read(&fb->refcount.refcount) > 1) {
+	if (drm_framebuffer_read_refcount(fb) > 1) {
 		drm_modeset_lock_all(dev);
 		/* remove from any CRTC */
 		drm_for_each_crtc(crtc, dev) {