drm/msm: fix NULL-deref on snapshot tear down

drm/msm: fix NULL-deref on snapshot tear down

commit a465353b9250802f87b97123e33a17f51277f0b1 upstream.

In case of early initialisation errors and on platforms that do not use
the DPU controller, the deinitilisation code can be called with the kms
pointer set to NULL.

Fixes: 98659487b845 ("drm/msm: add support to take dpu snapshot")
Cc: stable@vger.kernel.org      # 5.14
Cc: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/525099/
Link: https://lore.kernel.org/r/20230306100722.28485-4-johan+linaro@kernel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>