drm: cleanup: use drm_framebuffer_reference instead of a kref_get

drm_framebuffer_lookup() does a kref_get() for the framebuffer if it finds one
corresponding to the fb id passed to it. Use drm_framebuffer_reference() instead
for clarity since it's the function used in other places to take a reference.
Signed-off-by: Archit Taneja <archit@ti.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -412,7 +412,7 @@ struct drm_framebuffer *drm_framebuffer_lookup(struct drm_device *dev,
 	mutex_lock(&dev->mode_config.fb_lock);
 	fb = __drm_framebuffer_lookup(dev, id);
 	if (fb)
-		kref_get(&fb->refcount);
+		drm_framebuffer_reference(fb);
 	mutex_unlock(&dev->mode_config.fb_lock);
 
 	return fb;