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/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index 8e6b18c..2be88eb 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -878,7 +878,7 @@
 		seq_printf(s, "%3d: user size: %d x %d, depth %d, %d bpp, refcount %d\n",
 			   fb->base.id, fb->width, fb->height, fb->depth,
 			   fb->bits_per_pixel,
-			   atomic_read(&fb->refcount.refcount));
+			   drm_framebuffer_read_refcount(fb));
 	}
 
 	mutex_unlock(&drm->mode_config.fb_lock);