VBLANK interrupt is driven bu line buffer vcounter which is ahead of CRTC vcounter. Use an interrupt that fires at the actual CRTC vblank start boundry. Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com> Acked-by: Harry Wentland <Harry.Wentland@amd.com> Reviewed-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>