drm/msm: clean event_thread->worker in case of an error

drm/msm: clean event_thread->worker in case of an error

If worker creation fails, nullify the event_thread->worker, so that
msm_drm_uninit() doesn't try accessing invalid memory location. While we
are at it, remove duplicate assignment to the ret variable.

Fixes: 1041dee2178f ("drm/msm: use kthread_create_worker instead of kthread_run")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/490106/
Link: https://lore.kernel.org/r/20220617233328.1143665-2-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>