drm/msm: Set drvdata to NULL when msm_drm_init() fails

We should set the platform device's driver data to NULL here so that
code doesn't assume the struct drm_device pointer is valid when it could
have been destroyed. The lifetime of this pointer is managed by a kref
but when msm_drm_init() fails we call drm_dev_put() on the pointer which
will free the pointer's memory. This driver uses the component model, so
there's sort of two "probes" in this file, one for the platform device
i.e. msm_pdev_probe() and one for the component i.e. msm_drm_bind(). The
msm_drm_bind() code is using the platform device's driver data to store
struct drm_device so the two functions are intertwined.

This relationship becomes a problem for msm_pdev_shutdown() when it
tests the NULL-ness of the pointer to see if it should call
drm_atomic_helper_shutdown(). The NULL test is a proxy check for if the
pointer has been freed by kref_put(). If the drm_device has been
destroyed, then we shouldn't call the shutdown helper, and we know that
is the case if msm_drm_init() failed, therefore set the driver data to
NULL so that this pointer liveness is tracked properly.

Fixes: 9d5cbf5f ("drm/msm: add shutdown support for display platform_driver")
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Krishna Manikandan <mkrishn@codeaurora.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Message-Id: <20210325212822.3663144-1-swboyd@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>