drm/msm/mdp5: Return error code in mdp5_pipe_release when deadlock is detected

mdp5_get_global_state runs the risk of hitting a -EDEADLK when acquiring
the modeset lock, but currently mdp5_pipe_release doesn't check for if
an error is returned. Because of this, there is a possibility of
mdp5_pipe_release hitting a NULL dereference error.

To avoid this, let's have mdp5_pipe_release check if
mdp5_get_global_state returns an error and propogate that error.

Changes since v1:
- Separated declaration and initialization of *new_state to avoid
  compiler warning
- Fixed some spelling mistakes in commit message

Changes since v2:
- Return 0 in case where hwpipe is NULL as this is considered normal
  behavior
- Added 2nd patch in series to fix a similar NULL dereference issue in
  mdp5_mixer_release

Reported-by: Tomeu Vizoso <[email protected]>
Signed-off-by: Jessica Zhang <[email protected]>
Fixes: 7907a0d77cb4 ("drm/msm/mdp5: Use the new private_obj state")
Reviewed-by: Rob Clark <[email protected]>
Reviewed-by: Dmitry Baryshkov <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/485179/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Baryshkov <[email protected]>

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