drm/msm: dpu: Use atomic_disable for dpu_crtc_disable

Matches dpu_crtc_enable and we'll need the old state in a future patch

Changes in v2:
- None

Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

Signed-off-by: Rob Clark <robdclark@gmail.com>