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

In the Linux kernel, the following vulnerability has been resolved:

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

Patchwork: https://patchwork.freedesktop.org/patch/485179/