drm/msm/mdp5: Return error code in mdp5_mixer_release when deadlock is detected

drm/msm/mdp5: Return error code in mdp5_mixer_release when deadlock is detected

There is a possibility for mdp5_get_global_state to return
-EDEADLK when acquiring the modeset lock, but currently global_state in
mdp5_mixer_release doesn't check for if an error is returned.

To avoid a NULL dereference error, let's have mdp5_mixer_release
check if an error is returned and propagate that error.

Reported-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Fixes: 7907a0d77cb4 ("drm/msm/mdp5: Use the new private_obj state")
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/485181/
Link: https://lore.kernel.org/r/20220505214051.155-2-quic_jesszhan@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>