drm/msm/mdp5: Don't leak some plane state

Apparently no one noticed that mdp5 plane states leak like a sieve
ever since we introduced plane_state->commit refcount a few years ago
in 21a01abb ("drm/atomic: Fix freeing connector/plane state too
early by tracking commits, v3.")

Fix it by using the right helpers.

Fixes: 21a01abb ("drm/atomic: Fix freeing connector/plane state too early by tracking commits, v3.")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Reported-and-tested-by:  <dorum@noisolation.com>
Cc: dorum@noisolation.com
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/551236/
Link: https://lore.kernel.org/r/20230803204521.928582-1-daniel.vetter@ffwll.ch


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>