commit e6db9579 upstream.

The DRM core used to only call prepare_fb/cleanup_fb() when a plane's
framebuffer changed, which achieved the desired effect.

It's apparently now up to the driver to decide on its own.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>